US and Iraqi troops backed by aircraft have been engaged in fierce clashes with Sunni fighters in central Baghdad.

Iraq's defense ministry said some 50 suspected insurgents had been killed in the battle around Haifa Street.

"Today's operation was designed to purge Haifa Street and nearby neighborhoods from terrorists," said spokesman Maj Gen Ibrahim Shaker.

The fighting came days after Prime Minister Nouri Maliki promised tough action against illegal armed groups.

A spokesman for the US military said it had no "battle assessment" of Tuesday's fighting.

The joint US-Iraqi forces were backed by US fighter jets and military helicopters, which fired into the area, witnesses said.

A steady barrage of mortar and machine-gun fire was heard along the west bank of the Tigris.

Police sources told the BBC that the Haifa Street clashes follow two days of violence in the Sunni stronghold, after an Iraqi army unit found 27 bodies dumped in the nearby Sheikh Marouf cemetery

The military reportedly sent troops to arrest those responsible for the killings, triggering the clashes.

'Foreigners' arrested

Early on Tuesday morning, gunmen attacked Iraqi military checkpoints leading to the cemetery.

The Iraqi forces called for support from their US counterparts, and together they sealed off the district and began house-to-house raids.

An interior ministry spokesman said 11 people had been arrested, including seven Syrian nationals.

The Haifa Street clashes broke out hours after Mr Maliki announced a new security plan for Baghdad.

The BBC's Peter Greste in Baghdad says it is not clear whether the current raids are a part of that plan.

"This area has been subject to insurgent activity which has repeatedly disrupted Iraqi security force operation in central Baghdad," US spokesmen Lt Col Scott Bleichwehl said in a statement.

Photo caption

Smoke rises over western Baghdad