Police officials say gunmen in two pickups sprayed the car of Bassem Mahmoud with bullets near the city of Baqouba, 60 kilometers northeast of the Iraqi capital. Baqouba is the provincial capital of Diyala.
Bassem headed a Sunni group known as Sahwa, which joined the fight against al-Qaida during the height of Iraq war.
A health official confirmed the deaths. All officials spoke on condition of anonymity because they are not authorized to talk to media.