Baghdad: About 50 insurgents mounted a brazen attack on Iraqi forces in Baghdad on Monday, prompting US troops to provide support in a battle that lasted seven hours, a US military spokesman said.

The guerrillas attacked Iraqi forces in the mostly Sunni Arab district of Adhamiya in northern Baghdad overnight. Five rebels were killed and one member of the Iraqi forces was wounded. There were no US casualties, said the spokesman.

"It was quite a battle. It lasted seven hours," he said.

While insurgents mount such attacks in their strongholds in western Anbar province, they are rare in the Iraqi capital.

Anbar was largely spared the wave of sectarian violence which has swept much of Iraq since the February 22 bombing of a Shiite shrine in Samarra - largely because the province is overwhelmingly Sunni.

Most of the sectarian violence has occurred in Baghdad and other religiously mixed areas. A Shiite cleric was killed Monday night in southwest Baghdad during a drive-by shooting, police said.

The US military also said insurgent attacks at a government centre and mosque were repulsed on Monday in Ramadi, west of Baghdad.

The attacks involved "multiple homicide car bombs, mortars, rocket-propelled grenades, and heavy machine gun and small arms fire ... and appeared to be closely coordinated," a military statement said.

The bold attack in Baghdad raises fresh questions about security in the capital as Iraqi leaders struggle to form a unity government they hope can avert a sectarian civil war.

The withdrawal of US troops depends on the performance of Iraq's security forces, who are struggling to curb insurgent suicide bombings, shootings and assassinations as well as a rise in sectarian violence.

Adhamiya residents said Shiite militiamen accompanied the Iraqi forces. That could not be independently confirmed.

Sunni leaders have accused the Shiite-led Interior Ministry of sanctioning militia death squads, a charge the government denies.

"Adhamiya residents have taken up arms to prevent the Shiite militia from entering. There are bodies on Omar bin Abdul Aziz street, but police forces can't get to the area," said the police official.

It was not clear if the bodies were civilians, insurgents or government forces.