An al-Qaeda affiliated group has claimed responsibility for carrying out an ambush that killed 48 Syrian soldiers and nine Iraq guards state employees in Iraq's Anbar province last week.

In a statement posted online on Monday, the Islamic State of Iraq, al-Qaeda's wing in Iraq, said the presence of Syrian government forces in Iraq proved collusion between the Shia-led government in Baghdad and Syrian President Bashar al-Assad.

"Military detachments succeeded in annihilating an entire column of the Safavid army," the group said referring to the dynasty that ruled Shia Iran from the 16th to 18th centuries.

Tehran is the closest regional ally of Assad, whose Alawite faith is an offshoot of Shia Islam.

"The lions of the desert and the men entrusted with difficult missions laid ambushes on the road leading to the crossing," the group said.

Last week, gunmen attacked a convoy of Syrians who had fled Yaarabiya across the border from Iraq to escape advancing Syrian rebels.

The Syrians, some of them wounded, were being escorted back home by Iraqi guards through the western province of Anbar, Iraq's Sunni Muslim heartland.

Iraq's defence ministry had earlier blamed the attack on Syrian armed groups it said had infiltrated the country.

Iraqi spillover

The civil war in Syria, where rebels are fighting to topple Assad, is straining Iraq's own precarious sectarian and ethnic balance of Sunnis, Shias and Kurds.

Since December, tens of thousands of Sunni protesters in Iraq have staged demonstrations, mostly in Anbar province, venting frustrations against Shia Prime Minister Nuri al-Maliki, who has close ties with Iran.

Iraq has said it takes no side in the Syrian conflict, but Ali Mussawi, a spokesman of al-Maliki, raised fears that the conflict in Syria is spilling over to Iraq.

While violence in Iraq has eased since the sectarian slaughter that killed tens of thousands in 2006-2007, bombings and killings still jolt the the country daily, often targeting Shia areas and local security forces.

On Monday, three people including two policemen were killed when a suicide bomber detonated explosives in a vehicle outside a police station in Dibis, 250km north of Baghdad.

Suicide bombs are the hallmark of Islamic State of Iraq.

A series of shootings across Baghdad killed a further four people including a policeman and a government-backed "Sahwa" fighter, militiamen who have been targeted for siding with the Shia-led Iraqi government.

In the northern city of Mosul, another policeman was killed in a roadside bomb explosion and in the town of Rutba, 360km west of Baghdad, gunmen on Sunday shot and killed the mayor there.

Also late on Sunday, five members of the same family were killed in Shirqat, 300km north of Baghdad.