The United Nations has pulled all its staff on a Polio eradication campaign in Pakistan out of the country after two more workers were killed on Wednesday.
The UN confirmed the withdrawal of its workers off the country's streets after the latest shootings in three separate incidents.
An injured Pakistani polio worker is treated at a local hospital in Peshawar on Wednesday
In the north-west area of Charsadda, a woman and her driver were shot by men on motorbikes, said senior government official Syed Zafar Ali Shah. He said gunmen targeted two other polio teams in the same town, but no one was wounded in those attacks.
In the nearby provincial capital of Peshawar, a male health worker is in a critical condition after being shot and badly wounded. Other UN health staff were targeted in Nowshera but fortunately escaped unscathed.
No group has claimed responsibility for the attacks which authorities say were co-ordinated and occurred at the same time in different parts of the country.
Speaking to Al Jazeera, senior police officer Shahid Hayat blamed "militants who issued a fatwa against polio vaccination in the past" for the killings.
In June the Taliban banned immunisations in the tribal region of Waziristan, condemning the polio campaign as a cover for espionage.
A Pakistani health worker marks an infant after immunisation with anti-polio drops in the slums of Lahore
However, a spokesman for the Pakistani Taliban, Ihsanullah Ihsan, told Reuters his group was not involved in the violence in spite of the organisation's repeated threats against the polio campaign. UN workers have received calls telling them to stop working with the 'infidels'.
A spokesman for the UN Children's Fund (UNICEF) and the UN World Health Organisation, Michael Coleman, told AFP that the two organisations halted polio work in Sindh and Khyber Pakhtunkhwa provinces on Tuesday after attacks in Karachi and Peshawar, but extended the suspension nationwide after the latest attacks.
Pakistani rescue workers carry the dead body of one of the polio workers killed by gunmen in Karachi
Six female workers were killed on Monday and Tuesday in attacks in Karachi and Peshawar, deaths which UN spokesman, Martin Nesirky, condemned as "senseless and inexcusable".
His words were followed by a joint statement from the UN World Health Organisation and UNICEF, which said that those killed were "among thousands who work selflessly across Pakistan to eradicate polio" and called on community leaders to create a secure environment for health workers to operate.
"Such attacks deprive Pakistan's most vulnerable populations - especially children - of basic life-saving health interventions," they added.
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