The incident took place on Friday, when a roadside bomb exploded near a federal police vehicle outside the town of Daquq, some 250 km north of the capital Baghdad, the source told Xinhua news agency.
The explosion also resulted in the destruction of the police vehicle, the source added.
Following the deadly attack, a joint force of the Iraqi army and police combed through the area to track down the attackers, he added.
The security situation in Iraq has been improved since security forces fully defeated the Islamic State (IANS) terror group in 2017.
However, IS remnants have since retreated to deserts and rugged areas, carrying out frequent guerilla attacks against security forces and civilians.