A suicide bomber driving a car packed with explosives blew himself up near a Kurdish security forces patrol killing at least eight of them early on Sunday, police said.
The attack took place in the centre of the ethnically mixed town of Tuz Khurmato, 170 km (105 miles) north of the capital Baghdad, in a notoriously unstable region over which both the central government and autonomous Iraqi Kurdistan claim jurisdiction.
No group claimed responsibility but suicide bombings are the trademark of al Qaeda, which has been regaining momentum in its insurgency against the Shi'ite-led Baghdad government.
More than 4,000 people have been killed by militants in Iraq this year, of which more than 800 were killed in July alone, according to violence monitoring group Iraq Body Count.
Sectarian tensions across the region have been inflamed by the civil war in neighbouring Syria, putting growing strain on Iraq, where Kurds, Shi'ite and Sunni Muslims have yet to find a stable way of sharing power.
Sunni insurgents, including the al Qaeda-affiliated Islamic State of Iraq, have been recruiting from Iraq's Sunni minority, which resents Shi'ite domination of their country since the U.S.-led invasion that toppled Saddam Hussein in 2003.