Islamabad, Pakistan - At least one policeman has been killed and two others wounded after an improvised explosive device hit a police vehicle on its way to provide security to a polio vaccination team in northwestern Pakistan, police said.

The attack took place in the Kulachi area of the town of Dera Ismail Khan, about 255 kilometres (158 miles) south of provincial capital Peshawar, on Tuesday morning, police official Iqbal Baloch said.

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"A polio campaign is ongoing here. This vehicle was going from Kolachi to Maddi when ... some four kilometres [2.4 miles] from Maddi, there was an IED blast that killed Constable Riaz," Baloch told Al Jazeera.

Baloch said initial investigations indicated the bomb had been detonated using a manual fuse.

"This is a new trend we are seeing because jammers do not work on manual IED's. Remote[-controlled] IEDs can be blocked using jammers."

He said a policeman had been killed and two others wounded in the attack. A local hospital official, speaking on condition of anonymity because he was not authorised to speak to the media, confirmed the toll.

The attack is the latest violence to single out polio vaccination efforts in Pakistan, one of only three countries in the world where the debilitating neurodegenerative disease remains endemic.

The attack brings the toll from violence aimed at polio vaccination teams and their attendant security convoys to at least 101 killed since 2012, according to an Al Jazeera tally.

Many of those killed have been police officers on duty guarding polio vaccinators, who go door-to-door across Pakistan to vaccinate more than 35 million children.

The vaccination effort involves more than 265,000 polio vaccinators, with a further 100,000 security personnel assigned to guard them as they go about their duties.

Last year, Pakistan saw a spike in polio cases, with at least 144 cases reported from across the country, many of them in a cluster that includes the district of Dera Ismail Khan and the adjoining city of Bannu.

The year marked a sharp increase in polio cases, with only 12 cases reported in 2018 and eight in 2017, according to government data.

This year, 17 cases have been reported from across the country, the data shows, the majority from Khyber Pakhtunkhwa province, where Dera Ismail Khan is located.

Polio eradication officials told Al Jazeera the campaign was continuing in Dera Ismail Khan district, despite Tuesday's attack.