Gunmen shot dead a woman working on UN-backed polio vaccination efforts and her driver in northwestern Pakistan on Wednesday (local time), officials said, raising to eight the number of people killed in the last 48 hours who were part of the immunisation drive.
The attack on the woman was one of five that took place on polio workers in northwestern Pakistan on Wednesday. One male polio worker was critically wounded, while the others managed to escape unharmed.
The recent killings prompted the UN's public health arm to suspend work on the vaccination drive in two of Pakistan's four provinces Wednesday, a major setback for a campaign that international health officials consider vital to contain the crippling disease but which Taleban insurgents say is a cover for espionage.
No group has claimed responsibility for the attacks. Suspicion has fallen on the Pakistani Taleban because of their virulent opposition to the polio campaign, but the group's spokesman, Ahsanullah Ahsan, denied responsibility in a telephone call to The Associated Press.
Police say they have killed two militant suspects and arrested a dozen others in connection to the attacks but did not provide more details on their identities.
Pakistan is one of only three countries where polio is endemic. Prevention efforts have managed to reduce the number of cases in Pakistan by around 70 percent this year compared to 2011. But the recent violence threatens to reverse that progress.
Militants accuse health workers of acting as spies for the US and claim the vaccine makes children sterile. Taleban commanders in the troubled northwest tribal region have also said vaccinations can't go forward until the U.S. stops drone strikes in the country.
Insurgent opposition to the campaign grew last year after it was revealed that a Pakistani doctor ran a fake vaccination program to help the CIA track down al-Qaeda chief Osama bin Laden, who was hiding in the town of Abbottabad in the country's northwest.
The number of attacks this week on polio workers is unprecedented. They came as the government started a three-day vaccination drive Monday targeting high risk areas of the country, part of an effort to immunize millions of children under the age of five.
The deadliest of Wednesday's attacks occurred in the northwestern town of Charsadda, where the female polio worker and her driver were gunned down, said senior government official Syed Zafar Ali Shah. Gunmen attacked two other polio teams in Charsadda and one in the town of Nowshera, but no one was hurt in those attacks, he said.
Earlier in the day, gunmen shot a polio worker in the head in the city of Peshawar, wounding him critically, said Janbaz Afridi, a senior health official in surrounding Khyber Pakhtunkhwa province.
On Tuesday, gunmen killed five female polio workers - three of them teenagers - in a series of attacks in Karachi, the capital of southern Sindh province, and a village outside Peshawar. Two men who were working alongside the women were critically wounded in those attacks. A male polio worker was also shot to death in Karachi on Monday.
Police conducted a pair of operations in Karachi in the wake of the shootings in which they arrested a dozen suspects and killed two suspected militants, said senior police official Shahid Hayat.
Maryam Yunus, a spokeswoman for the UN World Health Organisation in Pakistan, said the group's polio staff have been pulled back from the field in Khyber Pakhtunkhwa and Sindh and asked to work from home until the vaccination campaign ends Wednesday.
Officials in Karachi temporarily suspended the vaccination campaign in the city after the shootings Tuesday, but the Khyber Pakhtunkhwa government plowed ahead, not wanting to be cowed by the violence.
Several dozen polio workers and human rights activists protested against the killings in Pakistan's capital, Islamabad, on Wednesday and demanded security for the field staff.
The Pakistani government and the UN also condemned the attacks, saying they deprive Pakistan's most vulnerable populations - specifically children - of basic life-saving health interventions. The UN said it was increasing security for its polio workers, but did not provide any details.
Polio usually infects children living in unsanitary conditions, attacks the nerves and can kill or paralyse. A total of 56 polio cases have been reported in Pakistan during 2012, down from 190 the previous year, according to the UN Most of the new cases in Pakistan are in the northwest, where the presence of militants makes it difficult to reach children.
The new campaign aimed to give oral polio drops to 34 million children under the age of five. Clerics and tribal elders were recruited to support polio vaccinations in an attempt to open up areas previously inaccessible to health workers.