Reports indicate victims of Wednesday's ambush in Dulaimat in Diyala province include police officers and Sunni fighters opposed to al-Qaida, CNN reported.
Officials said gunmen first attacked a checkpoint in the village, killing a policeman. They then ambushed reinforcements, killing another 11 policemen and Sunni Arab fighters.
Officials said a joint force of national police officers and members of a local Awakening Council were searching an agricultural area held by insurgents.
Iraqi and U.S. military were not involved with the patrol and weren't close enough to help once the 20-minute attack happened, a local Iraqi commander said.
"The problem is that most members of the police are from other provinces, so they do not have any idea about the terrain in this neighborhood," Lt. Col. Sabah al-Tamimi of the Diyala police told The New York Times.
The forces searching the area weren't battle-tested because they usually patrolled in safer areas, Tamimi said.
"Conducting operations in these areas without support from the Iraqi army or from the multinational forces is a suicide mission," the commander said.