Nine bodies and 10 severed heads were found on Tuesday in an abandoned field north of Baghdad in a region where US and Iraqi forces are pressing ahead with offensives against al Qaeda forces.

In the northern city of Mosul, a suicide car bomber killed one civilian and wounded 15 others in an attack on a US convoy, US and Iraqi security officials said.

The US military said none of its soldiers were wounded in the attack in Mosul, where extra Iraqi troops and police have been sent for a "decisive" final push against al Qaeda.

Five US soldiers were killed by a roadside bomb in a coordinated ambush in Mosul, 390 km (240 miles) north of Baghdad, on Monday.

Police made the gruesome discovery of the bodies and severed heads in a field in Muqdadiya, 90 km (55 miles) northeast of Baghdad in Diyala, one of Iraq's northern provinces where U.S.
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, police and hospital officials said.

The 10 heads found nearby were all also blindfolded, some with bullet wounds, said Ahmed Fouad, the chief of the morgue in Baquba hospital. Baquba is the provincial capital of ethnically and religiously mixed Diyala.

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 was launched early this month and takes in the southern outskirts of Baghdad.

Those operations included assaults by a brigade of 5,000 U.S. troops and a division of Iraqis around Muqdadiya, a fertile part of the Diyala River Valley.

On January 9, the commander of US forces in northern Iraq, Major-General Mark Hertling, said five severed heads had been found in Diyala.

All had messsages scrawled in blood in Arabic on the foreheads warning that volunteers working with US-backed neighbourhood patrol groups would suffer the same fate.

Sharp falls in violence across Iraq have been attributed to the neighbourhood units, formed by mainly Sunni Arab sheikhs who turned against al Qaeda because of its indiscriminate killings, and an 30,000 extra US troops deployed last year.

Attacks across Iraq have fallen 60 percent since last June, but northern Iraq remains the biggest security headache for U.S.
and Iraqi forces.

Al Qaeda, blamed for most large-scale attacks in Iraq, and other insurgents regrouped in the north after being squeezed out of their former strongholds in western Anbar province and from around Baghdad during security crackdowns last year.

Mosul, Iraq's third-largest city and capital of Nineveh province, has been in the spotlight after Prime Minister Nuri al-Maliki said last week that Iraqi forces were preparing for a "decisive" offensive against al Qaeda in Iraq.

This followed a huge blast last week in Mosul, regarded by US commanders as al Qaeda's last urban stronghold in Iraq, which killed up to 50 people and wounded 220.

The blast was in an unoccupied building which the U.S.
military said had been used by al Qaeda to store tonnes of weapons and explosives. - Reuters