ISLAMABAD, March 29 (Xinhua) -- One police officer was killed and three other police officers injured after unidentified militants opened fire on a police vehicle in Pakistan's northwest Khyber Pakhtunkhwa province, police sources said on Sunday.

The attack occurred in the Bannu district on Saturday evening while the police personnel were conducting routine patrol duties, the sources told Xinhua.

According to the sources, the militants ambushed the police mobile vehicle, killing one and injuring three others.

The injured and the body of the cop were shifted to the district headquarters hospital in Bannu.

The militants also set the police vehicle on fire and fled with three Kalashnikov rifles belonging to the police personnel, the sources added.

Security forces cordoned off the area and launched a search operation to trace the attackers.

No group has claimed responsibility for the attack yet. ■