A roadside bomb blast has killed two polio vaccination workers in Pakistan's north-western tribal region.
It is the latest in a series of such attacks which have now killed 19 in two months.
"The two-men team was visiting Mali Khel village in upper Kurram tribal region when an improvised explosive device planted along the roadside went off, killing them on the spot," said Jawad Ali, in charge of the campaign in Kurram.
He said the team had been visiting different areas which were not covered by a three-day campaign that ended Wednesday.
Local administration official Javaid Ullah confirmed the incident.
On Tuesday a policeman was shot dead while guarding two female polio vaccination workers in the north-western district of Swabi.
On January 1, seven staff members of a charity involved in education and health projects, including polio vaccinations, were killed in the same district.
And in December gunmen killed nine health workers carrying out polio vaccinations in Karachi and the northwest.
No one has claimed responsibility for any of the 19 killings yet, but the umbrella Taliban faction last year banned polio vaccinations in the tribal region of Waziristan, condemning the campaign as a cover for espionage.
Pakistan, Afghanistan and Nigeria are the only countries in the world 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.
But rumours about vaccines being a plot to sterilise Muslims have long dogged efforts to tackle the highly infectious disease.