A police officer says the fighters of the Sahwa or Awakening movement were attacked early Monday morning near the town of Dujail, 80 kilometers (50 miles) north of Baghdad. Two other Sahwa members were injured.
A health official confirmed the casualty figures. Both officials spoke on condition of anonymity as they were not authorized to release information.
The Sahwa are Sunni Arabs who joined forces with the U.S. military to fight al-Qaida at the height of Iraq's insurgency. They have been regular targets for Sunni insurgents who see them as traitors.
The shooting came a day after a wave of bombings and other attacks across Iraq killed at least 92 people.