Nine bodies and 10 severed heads were found today in a field north of Baghdad.
Police made the discovery in a field in Muqdadiya, 90km northeast of Baghdad in Diyala, one of Iraq's northern provinces where US and Iraqi forces are fighting Sunni Islamist al-Qaeda.
Police said some of the nine complete bodies were partially decomposed while others had been killed more recently. The bodies were all handcuffed and blindfolded and had bullet wounds, they said.
The 10 heads found nearby were all also blindfolded, some with bullet wounds.All had messages scrawled in blood in Arabic on the foreheads warning that volunteers working with US-backed neighbourhood patrol groups would suffer the same fate.
In the northern city of Mosul, a suicide car bomber killed one civilian and wounded 15 others in an attack on a US convoy, officials said. Five US soldiers were also killed by a roadside bomb in an ambush in Mosul.
About 24,000 US troops and 50,000 Iraqi soldiers are taking part in operations in Iraq's northern provinces, part of a wider offensive that began early this month and takes in the southern outskirts of Baghdad.
Attacks across Iraq have fallen 60 per cent since last June, but northern Iraq remains the biggest security headache for US and Iraqi forces.