KHAR, Pakistan — A Pakistani government official says gunmen have shot and killed a policeman assigned to protect polio workers in the country's northwest.

The killing comes amid a nationwide campaign aimed at vaccinating 38.6 million Pakistani children under the age of 5.

The official, Anwarul Haq, said that some suspects were detained following Monday's killing of officer Mohammad Sarfraz. The attack took place in the village of Badam in Bajur region, which borders Afghanistan.

Pakistan is one of few countries where polio is still endemic, along with Afghanistan and Nigeria.

Attacks on polio workers are common as the Taliban and militant groups claim the vaccination campaign against the crippling disease is part of a Western conspiracy.

No militant group immediately claimed responsibility for the latest attack.