"A monitoring team of the local health department was returning to their headquarters when unidentified gunmen hiding in the bushes along the roadside opened fire on their vehicle, killing two of them on the spot", local administrator Mahmood Aslam told AFP.
The attack had also claimed lives of two polio workers in the area.
The incident happened Saturday night in the Saafi area of the Mohmand tribal district, where authorities imposed a curfew and launched a search operation led by the paramilitary Frontier Corps.
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According to one member, he and the other driver were set free while two workers were shot.
Provincial Governor Iqbal Zafar Jhagra condemned the attack, calling the polio workers heroes. He said that the enemies of Pakistan can not bear to see the health factors of the country improve. Last month, a group of Pakistani polio workers was attacked by a school's administration in Karachi after the team attempted to vaccinate its students against the disease.
Pakistan, Afghanistan and Nigeria are the only countries in the world where polio is endemic, according to the World Health Organization and the Global Polio Eradication Initiative.
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Officials associated with the anti-polio campaign in the province believe they can not afford to abandon the efforts due to attacks and lose the gains they have obtained in the prolonged fight against polio.
Khan said the bodies of the polio workers were handed over to relatives and their funeral will take place later in the day.
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