A police officer stands guard as healthcare workers administer polio drops to a child during a door-to-door vaccination campaign in Peshawar. (AFP pic)PESHAWAR: Gunmen attacked a police vehicle assigned to protect a polio vaccination team, killing two officers and wounding another in Pakistan's northwest Khyber Pakhtunkhwa province on Tuesday, a police official told AFP.

Militants opened fire on the officers' vehicle while it was travelling near the Afghan border in Mohmand district, police official Ali Rehman Khan said, without specifying which group they believed was behind the attack.

"Two police personnel were martyred and another was injured in the attack.

"However, no polio vaccination staff were present in the police vehicle," he said.