29 October 2010 Last updated at 15:03 ET

by Emily Straton and Biodun Iginla, BBC News Analysts--Emily reported from London, and Biodun from New York

At least one UPS plane was isolated at Philadelphia airport

Security alerts are under way in the US, UK and Middle East after suspicious packages were found in Britain and Dubai.

The White House said the packages had been found overnight on two planes in transit to the US from Yemen.

Cargo planes were also searched at Newark in New Jersey, and Philadelphia.

A spokeswoman for the Jewish Federation in Chicago said the community had been warned to be on the alert in the wake of the discoveries.

"We were notified this morning that synagogues should be on the alert," the spokeswoman, Linda Haase, told Reuters news agency. "We are taking appropriate precautions and are advising local synagogues to do likewise."

The suspicious package in the UK was believed to be on its way to Chicago.

Al-Qaeda link?

New aviation security measures were being taken in light of the alert, the US Homeland Security Department announced.

The US is investigating whether the packages have any links to al-Qaeda's branch in Yemen - al-Qaeda in the Arabian Peninsula (AQAP).

Al-Qaeda and Jewish targets

April 2002: Suicide bombing at synagogue in Djerba, Tunisia kills 19. Al-Qaeda claims the attack
Nov 2002: 16 people killed in suicide bombing al-Qaeda claims to have carried out of Israeli-owned hotel in Mombasa, Kenya
May 2003: 45 killed in bomb attacks in Casablanca, Morocco, on targets including Jewish cultural centre. Group linked to al-Qaeda blamed.
Nov 2003: Two synagogues in Istanbul, Turkey, bombed, killing 23. Al-Qaeda claims responsibility
Oct 2005: Germany sentences four Arab men accused of links to al-Qaeda of planning attacks on Jewish targets

Live: Air cargo security alert

"If there is a nexus of terrorism then AQAP would have to be at the top of the list of suspects," a US official was quoted as telling Reuters news agency.

The White House said in a statement: "Based on close co-operation among US government agencies and with our foreign allies and partners, authorities were able to identify and examine two suspicious packages, one in London and one in Dubai.

"Both of these packages originated from Yemen. As a result of security precautions triggered by this threat, the additional measures were taken regarding the flights at Newark Liberty and Philadelphia International Airports."

The suspicious item found in the UK was reportedly an ink toner cartridge that had been modified.

According to the BBC's Home Affairs correspondent Daniel Sandford, it was not a "bomb" but was "potentially sinister".

At the scene

Laura Trevelyan BBC News, Newark airport

Cargo flights are seen as more vulnerable than passenger flights because the terminals tend to be in more remote locations so are more easily accessible.

This has been a worry ever since the 11 September attacks - that cargo planes could be an easier way for those who wish to attack the US to do so.

One of the most interesting things is what level of routine screening and supervision there is of cargo coming into the US.

It is very very difficult to screen everything, but cargo pilots have long felt themselves to be vulnerable: for a while they were asking if they could carry guns.

A suspect package from Yemen was also examined on a delivery truck in Brooklyn, New York, and later declared safe.

New York City Police Commissioner Ray Kelly said: "Obviously, examination of other packages are going on at other airports: Newark Airport, one. Philadelphia is the other one here. And some in Europe and in airports in the Middle East."

Emergency services were called to the UK airport in Donington, Leicestershire, overnight and evacuated a distribution centre, while the suspicious package was examined.

They closed off the freight distribution centre and a number of link roads.

The cordon was lifted only to be reimposed at 1400 BST (1300 GMT) for further investigations.

Planes isolated

The planes in the US were taken to remote locations to be searched.

At least one of the cargo planes being searched in the US was reportedly a UPS jet at Philadelphia.

"Out of an abundance of caution the planes were moved to a remote location where they are being met by law enforcement officials," said the TSA.

Earlier, US media reports suggested the suspicious package had been identified in London, but this proved to be incorrect.

Airports in London and around the rest of the UK were unaffected.

US security services remain on a high level of vigilance in the wake of the attempted Times Square bombing in May and the alleged attempted Christmas Day airliner bombing.

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by Emily Straton and Biodun Iginla, BBC News Analysts--Emily reported from London, and Biodun from New York

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