A police officer said the attack today took place when gunmen in three speeding pickup trucks fired on a security checkpoint manned by Sahwa fighters in the town of Tarmiyah, 50 kilometres north of Baghdad.
The police officer added that five other Sunni fighters and two civilians were wounded in the attack.
Medical officials confirmed the casualty figures. All officials spoke on condition of anonymity as they weren't authorised to release the information.
Insurgents frequently attack members of the Sahwa, which joined forces with US troops at the height of the Iraq war to fight al-Qaeda.