Military sources said 20 coalition have also died in the fighting.
Explosions and gunfire were heard in central Baghdad for a second straight night on Tuesday amid fighting between the US-led coalition and both Sunni insurgents and Shia radicals.
Heavy machinegun fire was heard for more than half an hour after a series of blasts rocked the capital at around 11:00 pm (1900 GMT).
A coalition spokesperson had no immediate comment on the source of the firing.
In the rebel stronghold of Fallujah west of Baghdad, street battles raged as US marines pressed a day-old offensive to flush out militants behind the brutal murder of four American civilians last week.
Marines fought guerrillas, their faces covered by headscarves, after tanks, amphibious assault vehicles and Humvees rolled into the western Iraqi town at 1:00 am (2100 GMT on Monday).
The force, backed by AC130 gunships and Cobra helicopters, took six hours to take control of the industrial area on the town's south-eastern outskirts amid sporadic attacks by insurgents firing mortars and assault rifles from rooftops, said Lieutenant Colonel Brennan Byrne.
During the operation, a number of insurgents were killed, Byrne said.
Five US marines were killed and eight wounded in separate attacks in Al-Anbar province, a mainly Sunni hotbed, since the marines launched an offensive on Fallujah on Monday, the US military said on Tuesday.
Another three US soldiers have been killed in separate attacks since Monday in a Shia district of Baghdad. The latest deaths raised to 20 the number of coalition troops killed since Sunday, including a Salvadoran, a Ukrainian and the rest Americans.
The US deaths raised to 616 the number of soldiers killed in action in Iraq since the US-led coalition invaded the country in March 2003 to oust president Saddam Hussein.
Late on Tuesday, fierce fighting erupted again between Italian coalition troops and militiamen loyal to firebrand Shia cleric Moqtada Sadr in southern Iraq, as Rome vowed its 3,000 soldiers in Iraq would not be driven out.
Sadr's Mehdi Army militia called a mid-afternoon cease-fire in the southern city of Nasiriyah, saying it was to allow the Italian soldiers to pull out of the area.
But by 6:30 pm (1430 GMT), gunfire was heard again in the centre of the city where 19 Italian paramilitary officers, soldiers and civilians died in a November bomb attack.
Twelve Italians were wounded earlier on Tuesday in gun battles during an operation to seize control of bridges in Nasiriyah from Sadr backers.
The Italians killed at least 10 Iraqis and wounded 37, according to figures from the city hospital.
A Bulgarian lorry driver was killed Tuesday when his convoy came under attack near Nasiyirah, his company said, while three Bulgarian and three Polish soldiers were reportedly wounded in an ambush in Karbala.
The Bulgarian, identified by his Sofia-based firm SO MAT only as a 41-year-old male, was in a six-lorry convoy protected by a British security company that came under attack from gunmen.
The Bulgarian soldiers, part of a 9,000-strong multinational force led by Poland, were wounded during a patrol near the holy city of Karbala.
The Polish military had previously reported two Bulgarian casualties in the Karbala attack, when troops were hit with mortar and automatic weapons fire.
In Baghdad's biggest Shia neighbourhood, US tanks and Humvees stood guard at strategic positions, including police stations, while US armoured columns cruised the teeming streets.
Soldiers atop tanks pointed their machine guns at the crowds as young militiamen from Sadr's outlawed Mehdi Army looked on defiantly.
At least 57 residents have been killed and 236 wounded in Sadr City, a sprawling slum home to more than two million people, since the US crackdown on Sadr's militiamen began on Sunday.
On Tuesday afternoon, US troops searched Sadr City offices, tearing down portraits of the firebrand cleric and his revered father, security guards said.
The soldiers were looking for weapons, guards Mohammed Haidar, 22, and Mustafa Haidar, 21, told AFP.
Witnesses said the US soldiers then walked into an adjacent mosque without removing their shoes, an act sacrilegious to Muslims.
A total of 106 Iraqis have been killed and 548 wounded in the clashes across the country between coalition forces and Sadr's Mehdi Army, which erupted on Sunday.
A Mehdi Army commander in Nasiriyah told AFP the militia had kidnapped two South Korean human rights workers there on Sunday and would not free them until Italian soldiers leave the city.
Officials in Seoul later said the pair had been released.
The coalition revealed on Monday that an arrest warrant was in force against Sadr, a member of a family of widely revered clerics, for the murder last April of a rival cleric days after Saddam Hussein's ouster.
Aides of the anti-coalition firebrand vowed that he would never be captured or surrender.
Hazem al-Araji, head of Sadr's office in Baghdad's Shia neighbourhood of Kadhimiya, told AFP the cleric "has left Kufa and is now in a place near the holy shrine of Imam Ali in central Najaf."
"We cannot give more details for security reasons," he said, adding that the cleric was "under the protection of his followers."
Amid the violence, UN special envoy Lakhdar Brahimi continued talks on Tuesday with Iraqi interim leaders. As fighting raged a day earlier, Brahimi said he hoped his talks here would help to keep the transfer to Iraqi sovereignty, set for June 30, on schedule.
And US overseer Paul Bremer said on Tuesday that Iraq's interim government will be put in place "well before" the June 30 deadline.