by Sunita Kureishi, BBC News Analyst, for the BBC's Biodun Iginla

The attackers are holding worshippers and priests in the church

Gunmen have taken around 40 worshippers hostage in a central Baghdad church, Iraqi police say.

The gunmen first attacked the stock exchange in the Iraqi capital before moving to a nearby Assyrian Catholic church, where a Sunday evening service was being held.

At least six people were killed in the attacks, police said.

The gunmen are reportedly demanding the release of al-Qaeda members imprisoned in Iraq and Egypt.

According to the police, several other people were wounded.

The attackers are also holding two priests at the Our Lady of Salvation Church, the Chaldean Bishop Shlemon Warduni told the AFP agency.

"What we know is that a number of worshippers and two priests are being held hostage at the church by terrorists," he said.

A local television station, al-Baghdadia, said it had been telephoned by the suspected attackers, who claimed they were from the organisation Islamic State of Iraq - an umbrella group embracing al-Qaeda and other militant groups.

The broadcaster said the men were demanding the release of al-Qaeda prisoners in Iraq and Egypt.

It reported that the men spoke in classical Arabic, which could imply that they are not from Iraq.

The BBC's Jim Muir in Baghdad said the church in Karada district was surrounded by security forces and the area sealed off.

There were reports that the gunmen threatened to shoot the hostages if the church is stormed by security forces.

In 2008, the Chaldean Catholic archbishop of Mosul, Paulos Faraj Rahho, was kidnapped by unknown gunmen and found dead two weeks later.