Friday's incident in Pakistan's Federally Administered Tribal Area (FARA) was the second in a week. Tribals view with suspicion and resent the immunization drive carried out by the government and NGOs.
The official, Abdul Ghani Khan, chief surgeon at the main government hospital in Bajur, was killed when a remote-controlled roadside bomb exploded in Salarzai, a village about 50 km northeast of Khar, the main town in Bajur Agency.
The blast killed Khan instantly, while it injured three in his car, local officials said.
Amir Khan, medical superintendent at the Khar District Headquarters Hospital, said residents of Mullah Said Banda in the Salarzai area had earlier refused to get their children vaccinated against polio and added that Ghani was visiting the area to allay misperceptions about the vaccination.
"The locals had also warned polio teams against visiting the area," Khan added.
Paramedic Hazrat Jamal, who is one of the three injured in the explosion, said that the residents of Mullah Said Banda were against the polio campaign.
"As soon as we reached there, an armed prayer leader warned us against visiting the area. Some locals said: 'On one hand, our enemy (a reference to the US) is bombing us for no reason while on the other hand you are coming here disguised as polio campaigners to spread vulgarity'," he told Daily Times at the hospital.
Bajaur Agency, on the troubled border with Afghanistan, is the hotbed of militant tribals, referred to as Pakistani Taliban.
No group has claimed responsibility for the explosion, but local tribal militants are suspected to be behind the attack.