PESHAWAR, Pakistan (AP) — Gunmen riding on a motorcycle shot and killed a policeman in northwestern Pakistan on Tuesday as he escorted a team of polio workers.

The attack in the district of Karak in Khyber Pakhtunkhwa province came on the second day of a nationwide anti-polio vaccination campaign that Pakistani authorities launched in an effort to eradicate the crippling disease by the end of the year.

The polio workers on the team in Karak escaped unharmed, according to local police officer Irfan Khan. A search for the attackers who fled the scene was underway, he added. No one immediately claimed responsibility for the attack.

Pakistan regularly launches polio drives. It had hoped to eliminate polio back in 2018, when only 12 cases were reported. But in the years since there has been an uptick in new cases. The latest five-day anti-polio drive started Monday, with the goal to vaccinate 40 million children across Pakistan.

Militants often target polio teams and police assigned to protect them. The Pakistani Taliban claim the campaigns are a Western conspiracy to sterilize children.

Pakistan and neighboring Afghanistan are the only two remaining countries in the world where polio is endemic, after Nigeria was last year declared free of the wild polio virus.