The bomber detonated an explosives-rigged vehicle near a three-vehicle police convoy in the town of Tuz Khurmatu, also wounding nine officers, district official Shalal Abdul Baban told AFP.
A doctor and police confirmed the toll.
The town is part of a swathe of northern territory that Kurds want to incorporate into their three-province autonomous region over the strong objections of the federal government in Baghdad -- a dispute that diplomats say is one of the main threats to the country's long-term stability.