At least two people have been killed after Iraqi security forces, backed by US troops, raided one of Baghdad's most important Sunni mosques.
Dozens of people were arrested during the raid
Eyewitnesses said clashes broke out when hundreds of troops entered Abu Hanifa mosque after Friday prayers.
The guards are said to have started shooting after shoes were thrown at them, a serious insult in Islam.
Iraq's interim government has said it will clamp down on those who "incite violence", including clerics.
The imam of the mosque was reported to be among dozens arrested there.
Several people were injured in the clashes.
The mosque, near the city centre, is associated with opposition to US-led coalition forces.
A policeman died in a Baghdad suicide attack
It is believed the security forces were looking for insurgents who escaped from Falluja during the US-led military assault, including foreign militants.
Witnesses said US military vehicles surrounded the building, but American troops did not appear to have gone inside. The mosque was not damaged.
Later, in a separate incident, one policeman was killed and several other people injured when a car bomb exploded in central Baghdad as an Iraqi police convoy drove past.
In other developments in Iraq:
- The International Committee of the Red
Cross criticises the "utter contempt" for humanity
shown by all sides in Iraq
- In the northern city of Mosul, Iraqi police backed by American troops arrest three people during a raid on a hospital after apparently being told that insurgents were treating their wounded there
- Iraqi police have arrested a senior aide to the radical Shia cleric Moqtada Sadr in the southern city of Najaf, his spokesman says
- One of the few remaining aid agencies in Iraq, World Vision, announces it is pulling out of the country.
It is now less than 10 weeks before elections are meant to be held across Iraq.
But the BBC's Caroline Hawley, in Baghdad, says some government officials are now expressing doubts they can be held on time with tension rising in Sunni parts of the country.
She adds that the Shia Muslim majority in Iraq wants elections so that they can turn their superior numbers into political power, but militants from the Sunni minority seem intent on disrupting the vote.
A state of emergency declared earlier this month is still in place and there are night-time curfews in several Iraqi cities.
Sporadic fighting has continued in the city of Falluja, a day after the senior US marine commander in Iraq, Lt Gen John Sattler, said the American-led offensive in the city had broken the back of the insurgency across Iraq.
American military officials say their forces have killed more than 1,200 insurgents in 12 days of fighting. Bodies left on the streets are being collected by an Iraqi civilian group for burial in mass graves.
The US military says it hopes to clear the city of insurgents in the next few days.
The US official overseeing reconstruction in Iraq, William Taylor, has said there are plans to spend $100m on reconstruction in Falluja once it is safe to start work there.
Mr Taylor added that the recent upsurge in violence had hampered reconstruction projects in Sunni-dominated parts of the country.
The US casualty toll in the Falluja offensive stands at
51 dead and about 425 wounded. Eight Iraqi government troops have also been killed.
The level of civilian casualties in Falluja is unknown.
The United Nations refugee agency has said that tens of thousands of people are thought to have been displaced by the fighting in Falluja.