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.Last Mod: 20 Eylül 2018, 18:16