The UN has halted its Pakistan polio vaccination campaign after two more of its workers were shot dead by Taliban gunmen.
A woman and her driver have been killed in north-western Pakistan just a day after similar attacks across the country killed five female polio workers.
The killings are a major setback for a campaign that international health officials consider vital to contain the crippling disease but which Taliban insurgents accuse health workers of acting as spies for the US and claim the vaccine makes children sterile.
In latest attack the woman and her driver were gunned down in the town of Charsadda. The gunmen targeted two other polio teams in the same town, but no one was wounded.
Earlier in Peshawar, gunmen shot a polio worker in the head, wounding him critically. There were also attacks on polio workers in the cities of Charsadda and Nowshera, but no casualties were reported there.
A spokeswoman for the World Health Organisation in Pakistan said their polio staff have been pulled back from the field and asked to work from home until the campaign ends.
WHO and Unicef condemned the attacks, saying they deprived Pakistan's most vulnerable populations - specifically children - of basic life-saving health interventions.
"We call on the leaders of the affected communities and everyone concerned to do their utmost to protect health workers and create a secure environment so that we can meet the health needs of the children of Pakistan," they said.
Pakistan is one of only three countries where polio is endemic.
The Taliban in the lawless north-western tribal region also blame the US drone strikes for their opposition to the vaccinations.
Yesterday gunmen killed five female polio workers in a series of attacks in several cities, at the time prompting authorities to suspend the vaccination campaign in the southern Sindh province.
The Khyber Pakhtunkhwa province has witnessed scores of attacks, most of them blamed on the Taliban.