Gunmen armed with silenced weapons attacked a house in a town north of Baghdad on Wednesday, killing seven members of a family, including three young children, security officials and a medic said.
Two members of the family, including one of the dead, belonged to the anti-Qaeda Sahwa militia force, made up of Sunni tribesmen who resisted the militant group and helped turn the tide of the war in Iraq.
The attack in the town of Tarmiyah took place about 4:00 am (0100 GMT). Among the dead were three children aged two, three and seven.
The violence comes a day after a wave of 15 bombings and a shooting in Iraq killed 19 people and wounded 71.
Violence in Iraq has decreased dramatically from its peak in 2006 and 2007, when brutal sectarian violence swept the country, but attacks remain common.
According to Iraqi government figures, 144 people were killed and 264 wounded in attacks last month.