The attack south of the sensitive shrine city of Samarra in Salaheddin province, where militants have overrun the state capital and a swathe of other territory, also wounded 25 people.
Samarra, 15 kilometres north of where the attack took place, is home to the revered Shiite Al-Askari shrine, which was bombed in February 2006, sparking a bloody Sunni-Shiite sectarian war.
The position was occupied by a mix of Iraqi soldiers and civilians who have volunteered to fight a major jihadist-led militant offensive that has overrun chunks of five provinces.
While government forces have since performed better, they are still struggling to carry out effective offensive operations against the militants.