Salahuddin provincial police say Friday's attack involved a roadside bomb that struck the pilgrim's bus near the town of Balad.
After the bomb exploded, gunmen opened fire on the bus from the roadside. Balad is 55 kilometers (50 miles) north of Baghdad.
Police say 14 people on the bus, including the Iraqi driver and the guide, were wounded in the attack. Medics at a nearby hospital confirmed the casualties. They spoke on condition of anonymity because they are not authorized to talk to the media.
Violence is down from 2006-2008, when Iraq seemed close to civil war. But deadly attacks against security forces and Shiite pilgrims are still frequent.