Iraqi police say they found nine severed heads wrapped in plastic bags near the town of Baquba Tuesday.
It was the second such discovery in recent days.
To the south, in Baghdad, a car bomb killed at least four people and wounded 12 others near a funeral reception. Earlier, an explosion near a taxi station killed one woman. Other attacks in Baghdad killed five other people Tuesday.
Insurgent and sectarian violence has increased across Iraq as Prime Minister Nouri al-Maliki struggles to fill two key cabinet positions responsible for security. Intense wrangling by factions within the governing coalition has blocked a consensus.
In other news, Mr. Maliki says he will order the release of 2,500 prisoners who were not involved in violence.
Also Tuesday, the U.S. military announced that an Iraqi army division has officially assumed control of territory in troubled Anbar province, near the town of Habbaniya, between Ramadi and Falluja. Anbar is a Sunni stronghold plagued by insurgent attacks. This is the first major transfer of territory in Anbar.
The U.S. military also says an American soldier was killed Monday by a bomb blast in Baghdad.