A Pakistani policeman was shot dead and another was wounded on Wednesday while escorting a polio vaccination team in the country's northwest, local officials said.
No one has claimed responsibility for the killings, but the Pakistani Taliban last year banned polio vaccinations in the tribal region of Waziristan, alleging the campaign was a cover for espionage.
Rumours about vaccines being a plot to sterilise Muslims have also dogged efforts to tackle the highly infectious disease.
Wednesday's killing happened in the Parhoti neighbourhood of the town of Mardan on the second day of a three-day local anti-polio campaign.
"One policeman was killed and other was wounded when two armed men riding a motorbike opened fire on the team comprising two females and one male member," senior local police official, Tahir Ayub told AFP.
He said that the members of polio team remained unhurt in the attack.
A senior local administration Zakaullah Khattak also confirmed the incident.
Pakistan, Afghanistan and Nigeria are the only countries where polio is endemic. Polio cases in Pakistan hit 198 in 2011, the highest figure for more than a decade and the most of any country in the world, according to the UN.
In January two polio vaccination workers, a policeman and seven members of a charity involved in polio vaccinations were shot dead in three separate incidents across the northwest.
In December gunmen killed nine health workers carrying out polio vaccinations in Karachi and the northwest.