Fierce fighting in the besieged Sunni stronghold of Falluja has led to the death of one US soldier and eight insurgents.
The fighting broke out after insurgents fired at US marines from a mosque that had been raided earlier by US forces.
The US troops replied with machineguns, jets and helicopters, and an imam accused the Americans of hitting his mosque.
Of the 522 US service personnel killed in action since the invasion in March 2003, more than 110 have died this month, many at Falluja.
Doctors in the town of 300,000 say some 600 people died in the three weeks since US forces retaliated for the murder of four American security guards.
In Najaf, the other main center of confrontation, 200 US troops entered the holy city, despite a plea from Iraq's senior Shia cleric not to. They army said it was not an offensive against Moqtada al-Sadr's encircled anti-American militia but merely to cover the withdrawal of Spanish troops.
The new Spanish government, elected after Madrid bombs were claimed by Muslims opposed to the occupation, is withdrawing.