Fighting between rebels and forces loyal to Libyan leader Col Muammar Gaddafi has been continuing in key cities after a fifth consecutive night of air strikes by international forces.
Overnight, several loud explosions were heard in the capital, Tripoli.
In the rebel-held city of Misrata, east of Tripoli, government tanks have been shelling the area near the hospital.
A French fighter has shot down a Libyan air force jet which was violating the no-fly zone, ABC News has reported.
There have also been reports of fierce fighting between rebels and pro-Gaddafi forces in strategic Ajdabiya.
Residents fleeing the town described shelling, gunfire and houses on fire.
Air strikes
There are reports of Western air strikes hitting the Tajura district of the capital, Libyan military sources and media have said.
And the French military has said French air strikes hit a Libyan air base in the interior of the country overnight.
The strikes hit a base about 250km (155 miles) south of the Libyan coastline, French military spokesman Col Thierry Burkhard told reporters. He did not give any further information on the location of the target or the damage.
Later on Thursday, Western military planes were reported to have hit the town of Sebha in southern Libya, according to residents and media reports.
Sebha, about 750km (480 miles) south of Tripoli, is a Gaddafi stronghold and home to an important military base.
An explosion was also reported overnight at a military base in the Tajura region east of Tripoli. Residents in the capital earlier said plumes of black smoke could be seen coming from an area near a military base, although this has not been independently confirmed.
Tanks return
In Misrata, Libya's third-largest city, witnesses had said on Wednesday that tanks had pulled back from their positions under air assault from international forces.
But later, residents said the tanks had rolled back into the city and resumed shelling.
Misrata resident Muhammad told the BBC many large explosions were heard overnight in the city: "Even now we continue to hear the aeroplanes circling the air above Misrata right now...
"Our major problem in Misrata is with the snipers. Gaddafi's forces have occupied the main street... which stretches from the town centre all the way to the highway and beyond. There are snipers all along the rooftops of that street. They are firing indiscriminately into the main street and the back streets. But the heavy artillery and shelling has stopped since yesterday [Wednesday]. In that sense, we are in a much better position."
Another resident has said pro-government forces have seized control of the city's port, where there are thousands of stranded foreign workers seeking to leave, Reuters news agency reported on Thursday.
The same resident has said Western air strikes hit government tanks on the outskirts of the city late on Wednesday, but tanks inside the city remain there and have not been hit.
Misrata has been besieged for several weeks, with reports that more than a dozen people were killed in the latest clashes.
John SimpsonWorld Affairs Editor, BBC News, Tripoli
After one particularly loud explosion during the night, a column of smoke was seen rising from the direction of a military base in the city. There have been various bursts of prolonged firing from the ground, completely useless in terms of hitting the planes or missiles involved, but often an indication that the defenders think they are coming under attack.
There are contradictory accounts about the effectiveness of coalition attacks on Col Gaddafi's forces outside the rebel-held town of Misrata. On Wednesday, pro-Gaddafi tanks seemed close to taking the town, but after a number of coalition air strikes, they appear to have been silenced. Still, there are suggestions that the tanks and artillery may have opened up again under cover of darkness.
Misrata is the last major town in western Libya that's been holding out against the pro-Gaddafi counter attack, so it's important from the coalition's point of view to protect it from falling.
It may take the coalition of international powers days or weeks to destroy Col Gaddafi's military, but it will not require months, French Foreign Minister Alain Juppe has told reporters.
Earlier, the US chief of staff for the mission in Libya insisted there had been no reports of civilian casualties caused by allied action.
Rear Admiral Gerard Hueber's comments came despite claims to the contrary by Col Gaddafi's government.
Operational control
Earlier, British Air Vice Marshal Greg Bagwell said Col Gaddafi's air force no longer existed as a fighting force.
AVM Bagwell said the allies could now operate "with near impunity" over the skies of Libya and were now applying unrelenting pressure on the Libyan armed forces.
"We are watching over the innocent people of Libya and ensuring that we protect them from attack," he said. "We have the Libyan ground forces under constant observation and we attack them whenever they threaten civilians or attack population centres."
His comments came as Nato members debated who should lead the intervention, with the US keen to hand over operational control to Nato.
Nato members have been holding talks about assuming responsibility for the no-fly zone over Libya, so far without agreement.
Turkey is an integral part of the naval blockade, but has expressed concern about the alliance taking over command of the no-fly zone from the US.
US Secretary of State Hillary Clinton has again urged Col Gaddafi to step down and leave Libya.
UN Secretary General Ban Ki-moon has urged all sides in Libya to cease hostilities. "All those who violate international humanitarian and human rights law will be held fully accountable," his spokesman Martin Nesirky said.
US Defence Secretary Robert Gates is in the Egyptian capital, Cairo, for talks on both Libya and Egypt's hoped-for transition to democracy following the fall of Hosni Mubarak.
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Fighting between rebels and forces loyal to Libyan leader Col Muammar Gaddafi has been continuing in key cities after a fifth consecutive night of air strikes by international forces.
Overnight, several loud explosions were heard in the capital, Tripoli.
In the rebel-held city of Misrata, east of Tripoli, government tanks have been shelling the area near the hospital.
A French fighter has shot down a Libyan air force jet which was violating the no-fly zone, ABC News has reported.
There have also been reports of fierce fighting between rebels and pro-Gaddafi forces in strategic Ajdabiya.
Residents fleeing the town described shelling, gunfire and houses on fire.
Air strikes
There are reports of Western air strikes hitting the Tajura district of the capital, Libyan military sources and media have said.
And the French military has said French air strikes hit a Libyan air base in the interior of the country overnight.
The strikes hit a base about 250km (155 miles) south of the Libyan coastline, French military spokesman Col Thierry Burkhard told reporters. He did not give any further information on the location of the target or the damage.
Later on Thursday, Western military planes were reported to have hit the town of Sebha in southern Libya, according to residents and media reports.
Sebha, about 750km (480 miles) south of Tripoli, is a Gaddafi stronghold and home to an important military base.
An explosion was also reported overnight at a military base in the Tajura region east of Tripoli. Residents in the capital earlier said plumes of black smoke could be seen coming from an area near a military base, although this has not been independently confirmed.
Tanks return
In Misrata, Libya's third-largest city, witnesses had said on Wednesday that tanks had pulled back from their positions under air assault from international forces.
But later, residents said the tanks had rolled back into the city and resumed shelling.
Misrata resident Muhammad told the BBC many large explosions were heard overnight in the city: "Even now we continue to hear the aeroplanes circling the air above Misrata right now...
"Our major problem in Misrata is with the snipers. Gaddafi's forces have occupied the main street... which stretches from the town centre all the way to the highway and beyond. There are snipers all along the rooftops of that street. They are firing indiscriminately into the main street and the back streets. But the heavy artillery and shelling has stopped since yesterday [Wednesday]. In that sense, we are in a much better position."
Another resident has said pro-government forces have seized control of the city's port, where there are thousands of stranded foreign workers seeking to leave, Reuters news agency reported on Thursday.
The same resident has said Western air strikes hit government tanks on the outskirts of the city late on Wednesday, but tanks inside the city remain there and have not been hit.
Misrata has been besieged for several weeks, with reports that more than a dozen people were killed in the latest clashes.
John SimpsonWorld Affairs Editor, BBC News, Tripoli
After one particularly loud explosion during the night, a column of smoke was seen rising from the direction of a military base in the city. There have been various bursts of prolonged firing from the ground, completely useless in terms of hitting the planes or missiles involved, but often an indication that the defenders think they are coming under attack.
There are contradictory accounts about the effectiveness of coalition attacks on Col Gaddafi's forces outside the rebel-held town of Misrata. On Wednesday, pro-Gaddafi tanks seemed close to taking the town, but after a number of coalition air strikes, they appear to have been silenced. Still, there are suggestions that the tanks and artillery may have opened up again under cover of darkness.
Misrata is the last major town in western Libya that's been holding out against the pro-Gaddafi counter attack, so it's important from the coalition's point of view to protect it from falling.
It may take the coalition of international powers days or weeks to destroy Col Gaddafi's military, but it will not require months, French Foreign Minister Alain Juppe has told reporters.
Earlier, the US chief of staff for the mission in Libya insisted there had been no reports of civilian casualties caused by allied action.
Rear Admiral Gerard Hueber's comments came despite claims to the contrary by Col Gaddafi's government.
Operational control
Earlier, British Air Vice Marshal Greg Bagwell said Col Gaddafi's air force no longer existed as a fighting force.
AVM Bagwell said the allies could now operate "with near impunity" over the skies of Libya and were now applying unrelenting pressure on the Libyan armed forces.
"We are watching over the innocent people of Libya and ensuring that we protect them from attack," he said. "We have the Libyan ground forces under constant observation and we attack them whenever they threaten civilians or attack population centres."
His comments came as Nato members debated who should lead the intervention, with the US keen to hand over operational control to Nato.
Nato members have been holding talks about assuming responsibility for the no-fly zone over Libya, so far without agreement.
Turkey is an integral part of the naval blockade, but has expressed concern about the alliance taking over command of the no-fly zone from the US.
US Secretary of State Hillary Clinton has again urged Col Gaddafi to step down and leave Libya.
UN Secretary General Ban Ki-moon has urged all sides in Libya to cease hostilities. "All those who violate international humanitarian and human rights law will be held fully accountable," his spokesman Martin Nesirky said.
US Defence Secretary Robert Gates is in the Egyptian capital, Cairo, for talks on both Libya and Egypt's hoped-for transition to democracy following the fall of Hosni Mubarak.
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A coalition of Western Allies has launched a series of airstrikes against military targets in Libya. US and British warships and submarines in the Mediterranean, as well as British, US and French fighter jets, took part in the raids.
More fighters are now being moved to forward positions, closer to Libya. British jets are flying down to southern Italy. Danish and Canadian jets are on standby in Corsica.
Pro-Gaddafi forces have attacked the Libyan rebel stronghold of Benghazi and their tanks have entered the city, a BBC journalist witnessed.
A jet also appears to have been shot down over the city despite a declared ceasefire and a UN no-fly resolution.
World leaders are meeting in Paris to discuss military action.
The rebel's leader has appealed to the international community to stop the pro-Gaddafi bombardment, but the government denies it is attacking.
Reports suggest hundreds of cars packed with people were fleeing the city eastwards as fighting spread.
"Now there is a bombardment by artillery and rockets on all districts of Benghazi," rebel leader Mustafa Abdul Jalil told Al Jazeera television. "There will be a catastrophe if the international community does not implement the resolutions of the UN Security Council.
UN Secretary General Ban Ki-moon says the world must "speak with one voice" on Libya.
The new UN resolution authorised "all necessary measures" to protect Libyan civilians.
Getting ready
The BBC's Ian Pannell saw the government tanks on a bridge inside Benghazi at around 1030 (0830 GMT).
Earlier, US President Barack Obama said forces loyal to Col Muammar Ghaddafi must stop attacking rebel areas or face military action.
"Gaddafi must stop his troops from advancing on Benghazi, pull them back from Ajdabiya, Misrata and Zawiya and establish water, electricity and gas supplies to all areas," he said on Friday.
Benghazi residents were woken up at 0530 by sounds of what rebels say was a bombardment of city.
Shortly after 0900 a fighter jet was hit - it is unclear by what, and we don't know who it belongs to, but it caught fire and plummeted to earth, where it exploded.
The plane hit the ground in the western side of Benghazi, bursting into flames. A huge pall of smoke is currently rising over the city.
It would seem that Col Gaddafi's announcement of a ceasefire has been completely ignored by his troops.
Diplomatic sources suggest world powers could start launching air-strikes on Libya within hours.
On Friday, Col Gaddafi's government declared a unilateral truce but there were reports that government offensives in rebel-held towns were continuing, and our correspondent says gunfire was also heard coming from the sea.
A rebel spokesman was quoted as saying the downed jet was a rebel plane which had been shot down by pro-government forces.
The United Nations refugee agency says it is preparing to receive 200,000 people fleeing the fighting, amid reports of hundreds of cars full of people heading for the Egyptian border, while others are attempting to flee on foot.
The first families had arrived at the Egyptian border, extremely frightened and traumatised, saying some of their homes have been completely flattened said UNHCR spokeswoman Elizabeth Tan.
While officially, Libya's government claims it is respecting its ceasefire, on the ground a darker reality is emerging, says the BBC's Kevin Connolly in the eastern city of Tobruk:
Col Gaddafi may be using the interlude being the UN resolution being passed and its being implemented to punish rebels for their uprising before the West can intervene
The Libyan leader may also be seeking to conceal his armoured columns in the streets of Benghazi, making it infinitely harder for allied forces to attack them
Second largest city in Libya with population of 670,000
Industrial centre important to Libya's economy due to imports of foodstuffs and manufactured products
Heavily bombed in World War II; later rebuilt with country's newly found oil wealth as a showpiece for modern Libya
Scene of violent anti-government protests last month; announced as HQ of rebel transitional council on 26 February
But a Libyan government spokesman said there had been "no attacks whatsoever on Benghazi".
"As we said, we are observing the ceasefire and we want international observers to come," said the spokesman, Mussa Ibrahim.
Mr Ibrahim quoted a letter from Col Gaddafi to President Sarkozy of France, UK Prime Minister David Cameron and Mr Ban, saying the UN resolution had no authority because it was interfering in Libya's internal affairs.
The Security Council vote called for an immediate ceasefire, and endorsed using force and imposing a no-fly zone to protect civilians.
The British and French, along with some Arab allies, are expected to play a leading role in the enforcement of the resolution.
The French ambassador to the UN, Gerard Araud, told the BBC that he expected military intervention within hours of Saturday's summit.
Mr Cameron - who is scheduled to meet Mr Sarkozy and US Secretary of State Hillary Clinton ahead of the summit - has said British war planes are being moved to bases in the region.
Strength of outrage
Saturday's summit will be hosted by Mr Sarkozy. Mrs Clinton will represent the Obama administration while Arab nations expected to be represented include Jordan, Morocco, Qatar and the United Arab Emirates.
BBC diplomatic correspondent Bridget Kendall says it is a chance to demonstrate to the Gaddafi government, and to the rest of the world, the strength of outrage at his actions and the determination to stop him.
The US Navy is deploying additional warships to the Mediterranean to support possible military action.
Click to play
President Obama: Colonel Gaddafi has received "ample warning"
The commander in charge of planning for the no-fly zone will be US Adm Samuel Locklear, the BBC's Mark Urban has learnt.
Denmark and Canada have said they will supply fighter jets, with Italy, Spain and France making air bases available.
Nato is already providing 24-hour surveillance over Libya with its Awacs planes.
Secretary-General Anders Fogh Rasmussen said Nato was "completing its planning to be ready to take appropriate action in support of the UN resolution as part of the broad international effort."
The US ambassador to the UN, Susan Rice, told CNN that Col Gaddafi was already in violation of the UN Security Council resolution.
Col Gaddafi has ruled Libya for more than 40 years.
An uprising against him began last month after long-time leaders of neighbouring Tunisia and Egypt were toppled.
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THERE are many similarities between Libya and Iraq. The landscape is crusty and pancake flat. The housing is similarly spartan, and relentlessly dun. Because of a history of sanctions and the caprice of their leadership, Libyans and Iraqis alike have benefitted little from their country’s oil wealth. Both suffer from neglect.Last night's UN Security Resolution 1973 adds another parallel: the imposition of a no-fly zone and authorisation of "all necessary means" to protect civilians. In Libya, that means strikes on Colonel Muammar Qaddafi's ground forces if they start to shell towns. It also sanctions ground attacks and strikes on Libyan naval vessels if they too are used for bombardment. France has suggested that airstrikes against the Libyan leader's forces could start within hours. David Cameron, the British prime minister, announced on Friday that British Tornado and Typhoon jets are being moved into place in readiness for any action in Libya.
In response to the resolution, the Libyan government has said it is declaring a ceasefire and calling a halt to all military operations, in accordance with the resolution's dictates about the protection of civilians. How much that really means remains to be seen. Both Britain and France have said that they will judge Colonel Qaddafi on his actions, not on his words. Nonetheless, a ceasefire may make it harder to justify bombing him.
In April 1991, the UN Security Council passed a resolution calling on Iraq to end the repression of its population, and America, Britain and France imposed a no-fly zone. It was already too late though for Iraq's southern Shia, who despite western support for their uprising, were left to the ravages of the Iraqi Republican Guard, and killed in their thousands. But the Kurds in the north gained their own autonomous safe haven.
As in Saddam Hussein’s Iraq, the UN decision comes too late for many Libyans. Libya's western towns have been muzzled by the colonel’s counter-attack. It will, however, bring relief to the east. Real or imagined, the fear of a chemical weapons drop that made easterners tremble has receded. Libyan families in the east who feared another Halabja, the town Saddam Hussein's MiG aircraft gassed in March 1988, can breathe more easily.
A no-fly zone also significantly redresses the balance in the conflict between the regime and the rebels. In a vast country four times the size of Iraq, air capability is critical to Tripoli's projection of central power. Even while bunkered in his Bab al-Aziziya military base, the colonel maintained his strategic depth. It enabled him to move troops and maintain supply lines across the oil-rich Sahara separating east from west. Without his aerial reach, his forces are as vulnerable to overstretch as the rebels.
On the battlefield, too, air power gave the colonel the tactical edge. Each time rebel and regime infantries clashed, air power was decisive. In the flat barren terrain, it enabled the colonel to observe and then bomb exposed rebel lines, sending his ragtag opposition positioned on main roads into retreat. Aerial bombardment, too, prevented ill-trained irregulars from regrouping each time they tried to mount an effective counter-attack.
Psychologically, the UN's endorsement of a no-fly zone (something the Kurds never had) is a major boon for the rebels. As the colonel's forces advanced and the international community appeared to dither, many Libyans who had thrown in their lot with the rebels began to waver. In Benghazi, the main rebel town, businessmen who had strung rebel flags from their balconies or stuck them on their cars quietly took them down. The colonel's revolutionary-committee loyalists resurfaced in rebel-held areas, demanding pledges of allegiance from drivers trapped in traffic. Powerful tribal leaders in central Libya whose support could prove pivotal sat on the fence. Just as the colonel's curtain of fear had begun to descend once again, the promise of international protection will hoist it back up.
The danger remains of western military mission creep. Colonel Qaddafi might yet respond by lashing out wildly. In a television interview, he threatened to act as crazily as the external military forces stacked against him; and his defence-ministry spokesman suggested Tripoli might respond by attacking air or maritime traffic in the Mediterranean. But Iraqi precedent suggests otherwise. Saddam Hussein abided by the terms of a no-fly zone and grounded his planes, rather than risk drawing the west into a deeper conflict that might unseat him.
That said, a no-fly zone is by itself unlikely to deliver a rapid denouement, or achieve a cessation of violence. On the ground and at sea—thanks to Italy’s provision of speedboats—the colonel’s better trained, paid and armed troops still have the edge. They retain control of the west and much of the centre of the country, and from their frontline at Ajdabiya, the gateway to Benghazi, continue to cast a shadow over the rebel’s eastern holdings and the southern huge oil-fields. For their part, the rebels, hopeful of a more even fight, might use the reduced threat of aerial bombardment to redouble their efforts to march on Tripoli. Far from ending the conflict, the no-fly zone might extend the ground war amongst the oil installations and along well-trodden desert lines. Without or without mediation, the de facto division of Libya into an autonomous eastern safe haven and embittered West could be acquiring a more concrete form.
Libya's government is declaring an immediate ceasefire, hours after a UN Security Council resolution backed a no-fly zone over the country.
Libyan Foreign Minister Mussa Kussa said the ceasefire was intended "to protect civilians".
The UN resolution supported "all necessary measures" to protect civilians, short of an occupation.
Western powers had been discussing how to enforce the no-fly zone.
Before the announcement of the ceasefire, fighting between troops loyal to Libyan leader Col Muammar Gaddafi and rebel forces was reported to be continuing.
Pro-Gaddafi forces have launched a fierce attack on Libyan rebels in Zawiya, sources in the town say.
Casualties were reported as 50 tanks and 120 pick-up trucks launched three attacks on the rebel-held town 50km (30 miles) west of the capital, Tripoli.
Elsewhere, warplanes fired missiles on residential areas and near rebel positions in the oil port of Ras Lanuf.
Rebels say they have rejected an approach by officials offering to hold talks on an exit for the Libyan leader.
The Libyan leader had not sent anyone himself, but lawyers from Tripoli had volunteered to act as go-betweens, former Justice Minister Mustafa Abdel Jalil, who heads the rebels' Transitional National Council, told AFP.
Col Gaddafi has refused to cede power in the past, arguing that he has no official position and therefore it is impossible for him to resign.
In other developments:
UN High Commissioner for Refugees Antonio Guterres says the situation on Tunisia's border with Libya is now under control;110,000 people have flooded over the border since the crisis began, and some 14,000 Bangladeshis remain to be repatriated
UK Foreign Secretary William Hague says a no-fly zone over Libya is a practical possibility but needs broad international and legal support, adding that the UK and France were drafting a UN resolution on the issue as a "contingency"
Libyan state TV broadcasts footage of what is says are confessions from rebels captured in Bin Jawad. The men - blindfolded and with their hands tied - tell the cameras they were "persuaded" to fight, with one saying he went along "convinced that my action will destroy me and destroy Libya"
Under siege
Col Gaddafi's side believe they are making significant military gains, consolidating their hold on western Libya, says the BBC's Wyre Davies in Tripoli.
The rebels are firing off the guns all the time, probably to scare off Col Gaddafi's troops.
Earlier today, the bombing was quite accurate. Often in the past, you got the feeling that the pilots were deliberately missing.
But not today, when they bombed a house across the road from where we were filming. One of my colleagues was knocked over by the blast, although he is OK.
The more accurate bombing suggests the government has changed pilots or is giving different orders.
Yousef Shakir, an adviser to the Libyan cabinet, said: "The Libyan Army has, for the first time, taken a decision to cleanse the Libyan cities from rebels," he told the BBC. "The Army has already started in Libyan western cities and will move to Benghazi."
In western Libya, Zawiya and the opposition-held town of Misrata are still under siege from government forces.
Following Tuesday's onslaught in Zawiya, a source in the town said children as young as five were among the dead.
"I don't know how many are dead - they tore Zawiya down to ashes," a source in the town told the BBC.
On Monday, pro-Gaddafi forces had retaken the town of Bin Jawad, on the road to Ras Lanuf, which the rebels captured late last week.
On Tuesday, using air strikes, helicopter gunships and heavy armaments, they pushed back a rebel advance along the north coast, and more accurate attacks than had been seen previously seemed aimed at dislodging opposition fighters from a crossroads outside Ras Lanuf.
Rebel forces are not as well equipped as the pro-Gaddafi elements
Under these circumstances, it is difficult to see how the Gaddafi regime would be in any mood to compromise or talk about succession, our correspondent says.
A Libyan foreign ministry official described as "absolute nonsense" reports that Col Gaddafi had offered to stand down, Reuters reports.
The rebels believe the approaches are merely an attempt to divide the Gaddafi opponents.
There seems to be a division within the council, says the BBC's Mustafa Menhshawi in Benghazi, with some saying talks are under way between Col Gaddafi and rebel leaders to secure his departure from the country, while others deny any negotiations are being held.
The confusion within the rebel leadership is obvious, adds our correspondent, suggesting the council is not fully linked to rebel forces on the ground.
No-fly discussions
Western powers are stepping up their efforts to put in place a no-fly zone over Libya.
Britain and France are drafting a UN resolution, which will be debated by Nato defence ministers on Thursday.
Jalal al-Gallal from the National Libyan Transitional Council has told the BBC there has been no direct contact with the Gaddafi regime
The Organisation of the Islamic Conference, which represents Muslim countries, has joined the calls for a no-fly zone. Gulf Arab states gave their backing to the idea, condemning the use of violence against civilians by Libyan government forces and calling for an urgent meeting of the Arab League.
An Arab League official said the group's foreign ministers would meet on Saturday in Cairo to discuss the Libya crisis, Reuters reported.
A no-fly zone would probably ban military flights by government forces through Libyan airspace. Any aircraft violating the exclusion zone would risk being shot down by international forces.
No-fly zones were imposed on southern and northern Iraq in the wake of the first Gulf war in 1991, and during the war in Bosnia in 1994-95.
However, our correspondent in Tripoli cautions that any foreign intervention would have to be carefully calculated, as it risks playing into Col Gaddafi's hands.
The UN says more than 1,000 people have died and 200,000 have fled the violence in Libya, which is now in its third week.
Anti-Gaddafi rebels control most of the east of the country, centred around the city of Benghazi. However, the government has consolidated its hold on western areas and the capital, Tripoli, which is home to about a third of the population of 6.5 million.
The revolt against Col Gaddafi's 41-year rule is now well into its third week.
It comes in the wake of uprisings in Tunisia and Egypt, whose presidents were forced from power after mass street demonstrations.
Anti-government protests have also taken place in Bahrain, Yemen, Algeria and Jordan.
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Libyan government forces are advancing towards the oil port of Ras Lanuf, checking the rebels' westward progress, BBC correspondents say.
Bin Jawad, 50km (30 miles) from Ras Lanuf, has now fallen to forces loyal to Libyan leader Col Muammar Gaddafi.
The UN says 200,000 people have fled the violence in Libya, where the revolt is well into its third week.
Nato is considering military options in response to the situation in Libya, US President Barack Obama has said.
"We've got Nato consulting in Brussels around a wide range of potential options, including potential military options, in response to the violence that continues to take place in Libya," he said.
"We send a very clear message to the Libyan people that we will stand with them in the face of unwarranted violence and the continuing suppression of democratic ideals that we have seen there."
Migrants fleeing
Pro-Gaddafi forces launched multiple air strikes on Ras Lanuf on Monday.
John SimpsonBBC world affairs editor, Ras Lanuf, eastern Libya
The scale of the battle here may be small, but the importance for the future of Libya, and just possibly for the region, is great.
It is a mistake to see this campaign as an outright civil war. In skirmishes like those around Bin Jawad and Ras Lanuf, as few as 100 men are fighting on each side. Most are lightly armed, and even the aircraft which are used on the government side are remarkably ineffectual in their bombing - for whatever reason.
Yet if the rebels can get through to the city of Sirte, that will broaden the entire campaign. A majority of people in the city are said to favour Col Gaddafi, whose tribe comes from the area, but there is also said to be strong opposition to him in Sirte itself, and even - so it has been suggested - within his tribe.
If Sirte fell, the road to the anti-Gaddafi towns of the north-west would open up. If the rebels cannot fight their way as far as that, there would probably be stalemate and perhaps even an opening up of old east-west rivalries in Libya.
But at present the rebels have been checked at a small place which is scarcely marked on the maps. Bin Jawad remains the first real test of fighting quality between the two sides.
Mokhtar Dobrug, a rebel fighter who witnessed one air strike, told Reuters he had seen a plane firing two rockets.
A later air attack in the area saw a rocket destroying a car carrying a family, killing at least one person, Reuters quoted witnesses as saying, although it has not been possible to confirm the report.
Meanwhile, pro-Gaddafi forces launched a renewed tank and artillery attack on Zawiya, a rebel-held town 50km west of the capital, Reuters reported an exiled Libyan opposition group as saying.
Events in Libya were "absolutely outrageous", Nato Secretary General Anders Fogh Rasmussen told the BBC.
"These systematic attacks against the civilian population may, as stated by the UN Security Council, amount to a crime against humanity," he said.
However, he said Nato had no plans to intervene, and any operational role would be pursuant to a UN mandate.
Rebels have been trying to fight off a counter-offensive by Gaddafi forces, which have been attacking both near Tripoli and in the east after recent rebel gains.
The UN's latest figures show at least 191,748 people have fled the violence in Libya since the fighting began.
Many more are likely to want to leave but have not made it to a border or are constrained from crossing, said the UN Office for the Co-ordination of Humanitarian Affairs (Ocha).
Meanwhile, Col Gaddafi has warned that Libya plays a vital role in restraining illegal immigration to Europe from sub-Saharan Africa.
Up to 400,000 total projected to leave within three months
Total number of migrant workers in Libya: 2.5 million
Source: UN Office for the Co-ordination of Humanitarian Affairs
"There are millions of blacks who could come to the Mediterranean to cross to France and Italy, and Libya plays a role in security in the Mediterranean," he said in an interview with the France 24 television channel.
'Civilian targets'
UN Secretary General Ban Ki-moon has appointed Jordan's former foreign minister, Abdelilah al-Khatib, as his special envoy to Libya.
A statement from Mr Ban's office said he noted "that civilians are bearing the brunt of the violence, and calls for an immediate halt to the government's disproportionate use of force and indiscriminate attacks on civilian targets".
Mr Ban also said Libyan Foreign Minister Moussa Kusa had agreed to accept the immediate dispatch of a humanitarian assessment team to the capital.
The UN is launching an appeal for $162m (£99m) to help 600,000 people within Libya who are expected to need humanitarian aid, in addition to a projected total of 400,000 leaving the country in the short term.
UN relief co-ordinator Valerie Amos said that after heavy fighting in Misrata, 200km (125 miles) east of Tripoli, "people are injured and dying and need help immediately".
A local doctor told the BBC that 21 bodies and more than 100 wounded people had been brought to his hospital, which he said was also targeted by government troops.
Opposition spokesman Mohammed Benrasali witnessed a battle in Misrata
He said the fighting went on for at least six hours.
With a population of 300,000, Misrata is the largest town controlled by rebels outside their stronghold in the eastern part of the country.
Residents have called for the international community to establish a no-fly zone over Libya to prevent Col Gaddafi's air force from attacking.
The UK and France have drawn up elements of a UN resolution authorising such a no-fly zone, a British diplomat says.
This was contingency planning in case world leaders decided such a zone was necessary, the diplomat told the BBC: there were no current plans to table the resolution or launch negotiations.
Possible triggers for such a move might be a massive humanitarian emergency or gross and systematic violations of human rights, diplomats say.
Russian Foreign Minister Sergei Lavrov has reiterated his opposition to military intervention in Libya, the RIA Novosti news agency reports. Russia has the power to veto any UN Security Council resolution.
Key locations under control of pro- and anti-Gaddafi forces
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