Gunmen opened fire at a polio vaccination team in southwestern Pakistan Wednesday, killing at least four people and wounding several others.
Police say that three female health workers are among the dead.
The incident occurred in Quetta, the capital of violence-hit Baluchistan province.
A health worker wounded in the attack told reporters in a Quetta hospital that she was travelling in a van together with eight females and one male colleague to participate in the ongoing polio vaccination campaign when two gunmen riding a motorcycle intercepted their vehicle on the outskirts of the city and opened fire at them.
"The gunmen were firing at us and we kept crying for help but there were no police available," the woman said.
Prime Minister Nawaz Sharif has condemned the killing of polio workers. An official statement has quoted him as saying that "those targeting polio vaccinators are enemies of Pakistan."
Authorities say that attacks on polio vaccinators in Pakistan within the past four years have left nearly 70 people dead, including security personnel escorting the teams during national immunization drives.
The violence has undermined anti-polio efforts in Pakistan, where more than 85 percent of the worldwide cases are located this year, according to the World Health Organization.