Officers killed while on their way to accompany a polio vaccination team in northwest Lower Dir district.

At least two policemen have been killed in an attack targeting a polio vaccination drive in northwest Pakistan, officials say, the latest in a series of attacks targeting eradication efforts in one of only three countries in the world where the disease remains endemic.

The two officers were killed while on their way to accompany a polio vaccination team in the Lower Dir district, about 180 kilometres (112 miles) northwest of the capital Islamabad, early on Wednesday, local police official Faridullah told Al Jazeera by telephone.

“They had gone there to do their duty with the polio team,” said Faridullah, who goes by only one name. “Two policemen were killed. They were shot with pistols [and] we do not know how many attackers there were.”

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Pakistan has recorded at least 104 cases of polio this year, according to government data, a sharp increase from the 12 recorded in 2018 and eight the year before.

Polio eradication efforts have been hampered by a sharp spike in attacks targeting polio vaccination teams, with at least seven team members and policemen killed this year.

Since 2012, at least 98 people have been killed in attacks targeting polio vaccination teams in Pakistan, according to an Al Jazeera tally.

On Monday, Pakistan launched its latest National Immunisation Day, aiming to reach more than 39 million children under the age of five across the country with polio and other routine immunisations.

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More than 260,000 staff take part in each immunisation effort, which involves vaccination teams being sent door to door in every district across the country of 207 million people.

Following the attack, authorities said the polio vaccination campaign would continue to operate across the country, although it would be suspended in the Bishigram sub-district, where the attack occurred.

“Search operation is in progress in the area for the culprits/suspects by security agencies,” a statement said.

In April, a similar polio vaccination campaign was suspended across Khyber Pakhtunkhwa province, where Lower Dir is located, when false rumours regarding side-effects of the vaccine led a mob to riot, destroying a local health unit outside the provincial capital Peshawar.

Pakistan’s efforts to eradicate the debilitating disease, which targets children and can cause paralysis or loss of limb function, have been hampered for years by false rumours regarding the effects of the vaccine, including conspiracy theories alleging that it is part of a plot to sterilise or otherwise harm Muslims.

Worldwide efforts to eradicate the disease through the use of vaccine have largely been successful, reducing the number of cases from more than 350,000 in 1988 to 33 in 2018, according to the World Health Organization (WHO).

It remains endemic, however, in Pakistan, Afghanistan and Nigeria, although the West African nation has not reported a case since 2016.

Afghanistan has reported at least 22 cases of polio this year, according to the Global Polio Eradication Initiative (GPEI).