PESHAWAR, Pakistan — Gunmen killed a police officer Tuesday who was protecting a team of polio workers during a UN-backed vaccination campaign in northwestern Pakistan.
It was the latest of several attacks on Pakistani efforts to eradicate the deadly disease, found in only three countries in the world. Militant extremists view the vaccination campaigns as Western-backed plots to gain intelligence in sensitive areas and have frequently targeted the medical staff and those protecting polio teams.
No polio workers were wounded in Tuesday’s attack in the Mardan district of Khyber Pakhtunkhwa province, said police officer Fazal Wahid. At least two attackers were hiding in a field near a narrow road as the polio workers walked by on their way to visit houses, said Mardan Police Chief Inam Jan.
‘‘The polio workers were going door-to-door and one police officer was protecting them when the gunmen suddenly attacked them near an open area and fled,’’ Jan said, adding that the police were searching for the attackers.
No one immediately claimed responsibility for the attack and it wasn’t known whether the police officer was targeted because he was protecting the polio team or for some other reason.
Janbaz Afridi, a senior health official, said the polio vaccination campaign continued in various parts of the province Tuesday despite the killing. ‘‘We have taken best possible steps for the safety of polio teams,’’ he said.
In 2012, humanitarian workers, including those working to prevent the polio spread, were repeatedly targeted. According to UN figures, 19 humanitarian workers were killed last year in Pakistan. Of those deaths, 11 were related to polio eradication efforts, including several shootings in December when nine polio workers were killed across Pakistan.
In an effort to protect people administering the vaccine, the government has increasingly sent police officers into the field along with the vaccinator.
On Jan. 29, gunmen riding on a motorcycle killed a police officer protecting polio workers in the Swabi district in Khyber Pakhtunkhwa province.
Some militant groups oppose the vaccination campaign, accusing health workers of acting as spies for the United States or the Pakistani government. They are also angered since it became known that a Pakistani doctor helped in the United States hunt for Osama bin Laden.
The physician, Shakil Afridi, ran a hepatitis vaccination campaign on behalf of the CIA to collect blood samples from bin Laden’s family at a compound in northwestern city of Abbottabad, where US commandos killed the Al Qaeda leader in May 2011.
The samples were intended to help the United States match the family’s DNA to verify bin Laden’s presence there.
The campaigns are made more complicated by the fact that many Pakistani residents are also suspicious of the repeated vaccination efforts going on across the country and fear the vaccines are intended to make Muslim children sterile.
Pakistan is one of the few remaining countries, along with Afghanistan and Nigeria, where polio is rampant.