The gunmen used rocket-propelled grenades and machine guns in the attack, on a highway south of Kirkuk.

The city is home to Kurds, Arabs and Turkmen who claim the right to run the city and the oil-rich area around it.

There has been a recent upsurge in violence across Iraq - including Kirkuk. Last month 16 people died in a series of bomb attacks in the city.

The latest attack occurred at Rashaad, 38.6km (24 miles) south of Kirkuk, an Iraqi military official told Reuters news agency.