ISLAMABAD (AP) — Pakistani health officials say the country has suspended a nationwide anti-polio campaign after a health worker and two policemen escorting vaccination teams were killed in separate attacks across the country in less than a week.

Pakistan is one of three countries in the world where polio is still endemic. The other two are Afghanistan and Nigeria.

But militant threats and deep-rooted superstition have spurred many parents to refuse to vaccinate their children.

Officials say unidentified gunmen targeted polio workers and police assigned to protect them in three separate attacks this past week, in the heavily rural western regions bordering Afghanistan, before fleeing.

Saturday’s decision to halt the campaign against the crippling disease comes after two new polio cases were reported in the country’s northwestern province of Khyber Pakhtunkhwa.