Five health workers were shot dead in Pakistan on Tuesday as they helped immunize children against polio.
Four of the victims, all women, were killed in coordinated attacks across Karachi, Pakistan's largest city, the BBC reported.
A fifth woman, reportedly just 17 years old, was shot dead in the northwest city of Peshawar.
And at least one other male health worker was shot dead in Karachi on Monday.
All those killed were taking part in the World Health Organization's nationwide drive to eradicate polio, according to Reuters.
The campaign was due to run from Monday to Wednesday, but has been suspended in the Karachi region following the latest attacks.
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No one has yet claimed responsibility for the killings, but they follow repeated threats by the Taliban.
In June the group announced that it would not allow polio vaccinations in the tribal region of Waziristan, near the Afghan border, until the US ended its drone strikes on Pakistan.
Militant leaders also claimed that the program would be used as a cover for espionage – citing the example of Shakil Afridi, the Pakistani doctor who helped the CIA track down Osama bin Laden under the cover of going door-to-door to give hepatitis vaccinations.
A month later, a WHO doctor and his driver were shot as they attempted to deliver vaccines in Karachi. Other health workers were beaten up.
One Karachi health official told Reuters that before this latest vaccination drive, workers had received threatening phone calls warning them they would regret helping the "infidel" campaign.
Meanwhile Pakistani authorities have threatened to punish anyone in the tribal regions who refuses to allow their child to be immunized, Agence France Presse said. The penalties include having financial benefits cut off and being refused new ID papers.
Pakistan is one of only three countries in the world where polio remains endemic. Almost 200 children were paralyzed as a result of infection in 2011 alone, according to the BBC, the highest number in 15 years.
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