PESHAWAR, Pakistan (AP) — Gunmen riding on a motorcycle shot and killed a police officer protecting polio workers during a U.N.-backed vaccination campaign in northwestern Pakistan on Tuesday, the police said.

The attack took place as dozens of polio workers — including several women — were going door to door to vaccinate children in Gullu Dheri village of Swabi district in Khyber Pakhtunkhwa province, said senior police officer Izhar Shah. None of the polio workers the police officer was protecting were hurt in the attack, he said.