Gunmen have killed at least 35 people in an ambush to the north-east of the Iraqi capital Baghdad, officials say.
Reports say the victims include policemen and Sunni Arab fighters opposed to al-Qaeda.
The attack took place in a village close to the city of Baquba, in Diyala province, police said.
Diyala province has been the scene of sustained violence, and in July Iraqi forces - backed by the US - began an offensive to drive out insurgents.
Reports says that Wednesday's ambush happened at about 1530 local time (1230 GMT) in the village of Dulaimat.
Gunmen first attacked a checkpoint in the village, killing a policeman, officials said.
They then ambushed reinforcements, killing another 11 policemen and Sunni Arab fighters.
The dead included a police lieutenant-colonel and a police captain, a police official told Reuters news agency.
It is not clear if any civilians were also among the casualties.
US forces and the Iraqi army have since surrounded the area, but the gunmen were believed to have escaped, the official said.
Dr Ahmed Fuad, of Baquba hospital, said medics had received 20 dead.
"The bodies are riddled with bullets," he said.
Since September 2006 about 100,000 former anti-US Sunni Arab insurgents have joined so-called Awakening Councils, receiving salaries from the US.
Correspondents say the arrangements have made a huge difference to the security situation in Iraq.
But insurgents are thought to have regrouped in Diyala, prompting the major operation against them earlier this year.