Gunmen have shot five health workers on an anti-polio drive in a string of attacks in Pakistan, officials say, raising fears for the safety of workers immunising children against the crippling disease.
It was not clear who was behind the shootings but Taliban insurgents have repeatedly denounced the anti-polio campaign as a Western plot.
Health officials suspended the immunisation campaign in Karachi, Pakistan's biggest city of 18 million people.
Three women were killed and a man was wounded in two separate attacks on health workers in Karachi on Tuesday, said senior police superintendent police Imran Shaukat.
The team had received telephone calls warning workers they would regret helping the "infidel" campaign against polio, said health official Gul Naz, who oversees project in the area where the women were shot.
An anti-polio worker in Karachi was shot dead on Monday, the United Nations said.
In the northwestern city of Peshawar on Tuesday, gunmen on a motorbike shot a 17-year-old girl supervising an anti-polio campaign, said government official Javed Marwar.
She died of her wounds in hospital, a doctor said.
All of the victims were Pakistanis working with a UN-backed program to eradicate polio, which attacks the nervous system and can cause permanent paralysis within hours of infection.
It has been eradicated in all but a handful of countries but at least 35 children in Pakistan have been infected this year.
In Karachi, provincial Health Minister Saghir Ahmed said the government had told 24,000 polio workers it was suspending the anti-polio drive in the province.
Officials could not confirm if all the attacks were linked to the health campaign, said Matthew Coleman, a spokesman for the United Nations Children's Fund.
Many of the attacks occurred in areas notorious for gun violence but the situation was a worry, he said.
"We're concerned for the safety of front-line workers. They are the true heroes," he said.
There have been at least three other shootings involving polio eradication workers this year.
Some Islamists and Muslim preachers say the police vaccine is a Western plot to sterilise Muslims. Other religious leaders have taken part in campaigns aimed at debunking that myth.