New Delhi, April 14 -- Suspected militants opened fire on a vehicle carrying police officers assigned to protect polio workers in northwestern Pakistan on Tuesday, killing one of them and wounding four others before fleeing the scene, police said. Two attackers were killed when police returned fire.

The shooting occurred in Hangu, a district in Khyber Pakhtunkhwa province bordering Afghanistan, shortly after Pakistan launched its second nationwide anti-polio campaign of the year, according to local police official Mahmood Alam.

No group immediately claimed responsibility, but suspicion is likely to fall on the Pakistani Taliban and local militant groups, which often carry out similar attacks in the region and elsewhere. Pakistan and nei...