Gunmen have killed three Iraqi police officers in Baquba, north of Baghdad.
The mutilation of four Americans has raised tensions
The attackers reportedly fired on two police cars guarding a road junction, and threw a hand grenade at them.
The attacks, late on Thursday, came as the US vowed to bring to justice the killers of four US contractors whose bodies were mutilated by a mob.
Muslim leaders in the central Iraqi town of Falluja, where the attack happened, said they would use Friday prayers to condemn the incident.
The four contractors were ambushed and killed as they drove through Falluja, triggering scenes which have shocked America.
The bodies were dragged from the wreckage, hacked to pieces and two of them were hanged from a bridge.
In the Baquba attack, at least two Iraqi police officers were also injured.
Both Baquba and Falluja lie within the so-called Sunni triangle, a stronghold for insurgents fighting the US-led forces in Iraq.
The US-appointed Iraqi Governing Council has condemned the killings of the four Americans and said it would not "disrupt the march of our people toward the dawn of freedom and democracy".
A senior Falluja cleric said imams across the town would tell worshippers that the mutilation of the bodies was wrong.
"What happened in Falluja is a distortion of Islamic principles and it is forbidden in Islam," Sheik Khalid Ahmed told The Associated Press news agency.
The US has vowed justice for the dead Americans.
Top US military spokesman Mark Kimmit said coalition forces would re-establish control of Falluja - but he said force could be avoided if town authorities arrest those who carried out the murders.
"If they were to deliver these people to the criminal justice system, we will come back in and start the rebuilding of Falluja. That is their choice," he said.
Town leaders held a meeting late on Thursday and issued a statement condemning the mutilation of the dead bodies.
The leaders did not say whether they planned to take action against those involved in the violence.