PESHAWAR, Pakistan (AP) — Militants attacked a health center used in an ongoing anti-polio campaign in northwestern Pakistan on Tuesday, triggering a shootout that left two police officers dead, local authorities said. Three of the attackers were also killed in the exchange of fire.

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

Local police officer Adnan Khan said the attack happened in the morning as health workers were gathering ahead of leaving for the door-to-door campaign along with police, who escort polio teams for their safety.

No polio worker was harmed in Tuesday's attack but another police officer who was wounded later died at a hospital, Khan added.

The attack drew condemnation from the country's top political leadership, including President Asif Ali Zardari and Prime Minister Shehbaz Sharif, who paid tributes to the slain officers for bravely responding to the attack.

Also Tuesday, militants stormed a health center in North Waziristan, another former stronghold of the Pakistani Taliban in Khyber Pakhtunkhwa, snatched guns from officers and warned health workers who had gathered there not to take part in the anti-polio campaign, local police officer Shoib Khan said.

The attackers then left with the weapons they seized, he said, without offering more details.

Militants in Pakistan often target police and health workers during campaigns against polio, claiming the vaccination drives are a Western conspiracy 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 another nationwide polio drive to vaccinate 45 million children under age 5 after a surge in new cases. The campaign is the third this year.

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

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

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

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

In the latest attack, gunmen on Monday night fatally shot five construction workers assigned to repair a dam in Banjgur, a district in the southwestern Balochistan province, according to a government statement. It provided no further details, and it was not clear who was behind the attack.

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