Dozens of Iraqis and eight U.S. troops were killed in separate deadly clashes overnight between coalition forces and insurgents.

At least 15 Iraqis were killed in battle Monday night between British troops and followers of the radical Shiite cleric Muqtada al-Sadr, a coalition spokesperson said.

In Nasiriyah, gunmen opened fire on Italian forces patrolling the streets and bridges over the Euphrates, according to the Defence Ministry in Rome Tuesday.

Fifteen Iraqis were killed and at least 12 Italian troops were injured in the exchange of fire. Thirty-five Iraqis were also wounded.

A coalition spokesperson claimed Iraqi attackers used civilians as human shields during the attack. She said a woman and two children were among the dead.

Meanwhile in Baghdad, at least three hours of fighting between U.S. troops and supporters of al-Sadr also took a bloody toll.

Earlier in the day, the U.S.-led coalition had sent 1,200 marines and two battalions of Iraqi forces to seal off Fallujah as an operation code-named Vigilant Resolve began.

The mission is a crackdown on Sunni rebels believed responsible for an attack last week in which four American security contractors were killed and their bodies mutilated.

Fallujah has been placed under a night-time curfew and roads leading east to Baghdad have been closed indefinitely. Late Monday, residents reported seeing clashes on a highway north of Fallujah and gun battles in an industrial area of the city.

Campaigning in North Carolina on Monday, U.S. President George W. Bush vowed not to let the rising toll numbers deter his efforts to rebuild Iraq in the wake of the war he waged to topple leader Saddam Hussein.

But the deaths of more than 600 American soldiers in Iraq over the past 12 months is making him an easy target in this election year.

"Iraq is George Bush's Vietnam," prominent Democratic Senator Edward Kennedy said in a speech to the Brookings Institution Monday.

Republican politicians immediately labelled Kennedy's comments "vicious" and "outrageous."