R Reports - Ambulances take away the bodies of health workers in Karachi, Pakistan, shot by gunmen during an anti-polio drive on Tuesday.
Three women were killed and one man wounded in seperate shootings.
It was not clear who was behind the attack, but Taliban insurgents have repeatedly denounced the anti-polio immunisation campaign as a Western plot to sterilise Muslims.
The team had received telephone calls warning workers they would regret helping the "infidel" campaign against polio.
Another anti-polio worker in Karachi was shot dead on Monday.
And in the northwestern city of Peshawar on Tuesday, gunmen shot a 17-year-old girl supervising an anti-polio campaign there.
She later died in hospital.
Polio attacks the nervous system and can cause permanent paralysis within hours of infection.
At least 35 children in Pakistan have been infected this year.