An attack by unidentified assailants on a polio vaccination team in Mardan martyred two police officials, part of the team's security detail, on Wednesday.
A heavy contingent of police reached the area after the attack and cordoned it off. A search operation was also launched to apprehend the attacker.
The martyred personnel were identified as Syed Raza Ali Shah and Shakir, residents of Syedan tehsil and Mardan.
The bodies of the policemen were shifted to a nearby hospital, said DSP Adnan Azam Khan.
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Earlier this year, a security officer was martyred in a gun attack on a polio team in Karak. The polio team remained unhurt in the attack but the officer providing security to the team was shot and martyred.
There was no immediate claim of responsibility for Wednesday's killings.
Vaccination campaigns have faced stubborn resistance for years in Pakistan, with many refusing to have their children inoculated because of misinformation and conspiracy theories.
But as Pakistan tries to reach its goal of eliminating polio from its territory, a new challenge has emerged in the form of a growing global movement against vaccinations.
The phenomenon has attracted adherents worldwide, fuelled by medically baseless claims and proliferated by social media resulting in a resurgence of once-eradicated, highly contagious diseases.