UN agencies suspended polio vaccination field work in Pakistan Wednesday after two health workers were shot dead and one badly wounded, taking the death toll this week to eight, DPA reported
The World Health Organization (WHO), which partners with Pakistan's government in the polio eradication drive, blamed the "very precarious" security situation.
"Until we know better about the security situation, we are asking our staff to work at home," WHO's chief coordinator for the programme in Pakistan, Elias Durry, told dpa.
No one has claimed responsibility for the killings, but the Taliban has in the past threatened the polio campaign, charging that health workers are spies, amid rumours the drug causes infertility.
A Pakistani doctor used an anti-polio drive as cover to help US intelligence track down al-Qaeda leader Osama bin Laden in the northern town of Abbottabad last year.
Children's welfare agency UNICEF on Wednesday condemned the deadly attacks on Pakistani health workers.
"The government of Pakistan and the affected provinces have temporarily suspended the vaccination campaign due to concerns over the safety of health workers," the two UN agencies said.
But a senior government official said thousands of health workers directly reporting to it would continue their field work.
"WHO and UNICEF officials just provide additional support by monitoring the progress in the campaign," said Altaf Bosan, national coordinator for polio-monitoring in the prime minister's office.
On Wednesday, a female health worker supervising immunizations and her driver were shot dead in Charsadda, 35 kilometres north-east of Peshawar, capital of the north-western Khyber-Pakhtunkhwa province.
"Three masked gunmen on a motorcycle opened fire on the health worker's car, killing the woman and her driver on the spot," said senior police officer Zahir Shah.
A few hours earlier, a volunteer health worker was shot in the head while administering the oral vaccine during a door-to-door campaign in Peshawar, police spokesman Jalaluddin said.
Hilal Ahmed, in his early 20s, was on a ventilator after surgery for a bullet wound to the head, Iqbal Afridi, head of Peshawar's state-run Lady Reading Hospital, told dpa.
He was in a critical condition, other hospital officials said.
Two other attacks involving polio vaccinators were also reported in the province, but there were no casualties.
Six health workers were killed earlier this week, five of them in Karachi, capital of the southern province of Sindh, and one in Peshawar.
No group has claimed responsibility, but Islamist militants have opposed the vaccinations, and blocked the programme in the tribal region of Waziristan along the Afghan border this year.
Khyber-Pakhtunkhwa province's information minister, Mian Iftikhar Hussain, blamed Taliban-linked insurgents for the recent attacks.
The insurgents had a "special agenda," he said, "to make the world declare Pakistan a polio-endemic country, so that its people cannot go abroad and expatriates are sent back home," he said.
Pakistan is one of only three countries where polio is still considered endemic, along with Afghanistan and Nigeria.
WHO says 56 polio cases have been reported this year in Pakistan.
Female health workers held demonstrations in Karachi and the nearby town of Hyderabad against the killings, and called for action against the perpetrators.
German Development Minister Dirk Niebel urged Pakistan to take steps to resume the polio eradication campaign.
"The Pakistan government must do everything in its power to ensure that these immunizations are carried out," Niebel told dpa in Berlin. "Polio is a scourge of humanity that can be eradicated."