Eleven Iraqis were killed when they tried to ambush a US Army patrol in the northern town of Samarra on Tuesday.
Members of Task Force Ironhorse, part of the 4th Infantry Division, were on a patrol when they were attacked, CNN quoted military spokesperson Lt Bill McDonald as saying. A second patrol, operating nearby, helped repel the attack, he said, adding there were no American casualties.
The attack came on a day when supporters of ousted president Saddam Hussein protested against their leader's arrest.
Violence erupted in Ramadi, where about 750 people participated in a pro-Saddam rally. An American soldier was hurt and two Iraqis were killed, CNN said.
At the University of Mosul, up to 1,000 students demonstrated; in Falluja, hundreds of residents rioted, seizing the offices of the US-appointed mayor, the BBC said. One person was killed and three, including an American solider, were wounded, the BBC added.