PESHAWAR, Pakistan (AP) — Militants attacked a health center used in the ongoing anti-polio campaign in northwestern Pakistan on Tuesday, triggering a shootout that left a police officer dead, local officials said. Three of the attackers were killed in the conflict.

No one immediately claimed responsibility for the attack in Orakzai, a district of Khyber Pakhtunkhwa province and a former stronghold of the Pakistani Taliban.

Local police officer Adnan Khan said the attack took place in the morning as healthcare workers gathered for their safety before leaving for a door-to-door campaign, with police accompanying polio teams.

Khan added that no polio workers were harmed in Tuesday’s attack, but another police officer was injured.

Also Tuesday, local police officer Shoib said militants raided a health center in North Waziristan, another former Pakistani Taliban stronghold in Khyber Pakhtunkhwa, snatched the officers’ weapons and warned health workers gathered there not to join the anti-polio campaign . Khan said.

He said the attackers then left with the weapons they seized, without giving further details.

Militants in Pakistan frequently target police and health workers during anti-polio campaigns and claim that vaccination campaigns are a Western plot to sterilize children.

Pakistan and Afghanistan are the only two countries in the world where the spread of polio has never been stopped.

In severe cases, polio can cause permanent paralysis and death.

Pakistan on Monday launched a new nationwide polio campaign to vaccinate 45 million children under the age of 5 following a surge in new cases. The campaign is the third this year.

So far this year, Pakistan has recorded 41 cases in 71 districts, mostly in southwestern Balochistan and southern Sindh provinces, as well as Khyber Pakhtunkhwa and eastern Punjab province.

In Afghanistan, local health officials said on Monday that vaccinations have started in 16 of the country’s 34 provinces. According to spokesperson Sharafat Zaman, the campaign will last three days and target 6.2 million children under the age of 5.

According to the World Health Organization, there have been 23 confirmed cases in Afghanistan this year.

Insurgents and separatists also target security forces and civilians in various parts of the country.

In the latest attack, gunmen shot and killed five construction workers assigned to repair a dam in Banjgur district of southwestern Balochistan province on Monday night, according to a government statement. No further details were given and it was unclear who was behind the attack.

Associated Press writer Abdul Sattar in Quetta, Pakistan, contributed to this report.