SAMARRA: At least nine people were killed in clashes on Friday when militant gunmen drove two cars up to a checkpoint north of Baghdad and opened fire on members of an Iraqi government-backed militia guarding the post, police said.

Five "Sahwa" militia members and four militants were killed, including a suicide bomber whose explosive belt was detonated during the fighting which lasted about 20 minutes at the checkpoint in Samarra, 100 km (60 miles) north of the capital.

The Sahwa or Sons of Iraq are former Sunni insurgents who rebelled against al Qaeda in the Sunni heartland province of Anbar at the height of the Iraq war and helped American troops turn the tide of the conflict.

No group immediately claimed responsibility for the attack, but al Qaeda's affiliate Islamic State of Iraq often targets Sahwa militias, in retaliation for their co-operation with the Shi'ite-led government.

Iraq's precarious Sunni-Shi'ite balance has come under growing strain from unrest in the country's Sunni heartland and the increasingly sectarian civil war in neighbouring Syria.

Last month, gunmen riding motorbikes and wearing Iraqi army uniforms executed seven Sahwa members near the town of Tuz Khurmato, 170 km north of Baghdad.

That followed an attack earlier in February, when a suicide bomber dressed in civilian clothes infiltrated a meeting of Sahwa leaders and detonated his explosives as they picked up salaries in Taji, killing at least 22 people.

While violence has fallen from the height of the sectarian slaughter that killed tens of thousands in 2006-2007, insurgents remain active, carrying out daily attacks in a bid to destabilise the government.