The US military in Iraq has vowed to "destroy" the militia which backs a radical Shia cleric responsible for much of the latest wave of violence.
Sadr's Mehdi Army is thought to have about 10,000 members
US-led forces are already conducting operations against Moqtada Sadr's Mehdi Army, said a US military spokesman.
More than 100 Iraqis have died in three days of clashes in areas to the west and south of the capital, Baghdad.
About 20 coalition troops have also been killed, including 12 US marines in a single attack in the town of Ramadi.
Mr Sadr's Mehdi Army was created in the summer of 2003 and is thought to have up to 10,000 members.
- Eight Iraqis are killed in clashes with US troops during a demonstration near the northern city of Kirkuk, police say.
- Ukrainian troops pull out of the southern town of Kut after clashes with Mehdi Army militants.
- A US military helicopter is hit by small arms fire near the central town Baquba. The Americans say there are no reports of injuries.
- At least 36 Iraqis are said to have been killed in the past 24 hours in the flashpoint town of Falluja.
- Four Iraqis are reported to have been killed by US air strikes in Baghdad's Sadr City neighbourhood - up to 60 estimated to have been killed since Monday.
"In the central and southern regions of Iraq, the coalition and Iraqi security forces are conducting operations to destroy the Mehdi Army," US Brigadier General Mark Kimmitt told a news conference in Baghdad.
"Those attacks will be deliberate, precise and they will be successful."
An arrest warrant has been issued for the cleric on charges unrelated to the current violence.
Mr Sadr is currently surrounded by his gunmen who appear to control the holy city of Najaf.
They also control the towns of Kufa and Kut.
US troops have kept out of those cities, but are trying to hunt down the militiamen in the mainly Shia neighbourhood of Sadr City in Baghdad.
"If he [Mr Sadr] wants to calm the situation... he can turn himself in to a local Iraqi police station and he can face justice," Gen Kimmitt said.
The action by the Shias was triggered by the closure of Mr Sadr's al-Hawza newspaper a week ago on the grounds that it was inciting violence.
The Shia-led violence has opened a second front for US-led coalition troops who had previously been confronting mainly Sunni supporters of the former Iraqi leader, Saddam Hussein.
MAJOR US COMBAT LOSSES
6 April 2004: 12 marines killed and 20 injured at Ramadi
2 November 2003: helicopter shot down near Amiriya with 15 soldiers killed
23 March 2003: 29 soldiers killed at Nasiriya
On Monday, the US launched a big operation to "pacify" the town of Falluja - in the Sunni triangle that has been the centre of opposition to the occupation.
The operation follows last week's horrific killing of four US contractors whose bodies were dragged through the streets.
US President George W Bush has insisted the US resolve in Iraq remains "unshakable", despite the clashes.
The White House is now back on a war footing, the BBC's Justin Webb in Washington reports, and Secretary of State Colin Powell has urged the nation to rally behind its troops.