QUETTA, Pakistan (AP) — Pakistani police say gunmen riding on motorcycles opened fire on female polio vaccination workers in the southwestern town of Chaman, killing one and wounding the other.

Local police official Sami Agha says the assailants fled after Thursday’s attack, which was the third this week.

In separate attacks Tuesday and Wednesday, assailants killed two policemen assigned to the polio vaccination drive in the northwest.

Agha says the latest attack took place when the workers were visiting a residential area to give polio drops to children as part of a nationwide campaign to fight the crippling disease. Chaman is a border town in Baluchistan province.

Pakistan regularly carries out anti-polio drives, despite threats from the Taliban who claim the campaign is a Western conspiracy to sterilize children.