File photo: VCG

Three policemen and one driver were killed Tuesday night after unknown gunmen attacked a deputy governor's convoy in Nigeria's central state of Nasarawa, a police source told Xinhua.

The attack, according to the source, took place as Emmanuel Akabe, the deputy governor of Nasarawa, was on his way to Abuja to attend the swearing-in ceremony for ministers scheduled for Wednesday.

Confirming the incident, state police spokesman Othman Ismaeel told Xinhua over phone that he was yet to be fully briefed, as the state police chief and other senior officers were still at the scene.