Pakistani authorities say gunmen shot and killed a mother and her daughter who were taking part in an antipolio campaign in the southwestern city of Quetta.
Police official Naseebullah Khan said that Sakina Bibi, 50, and her 20-year-old daughter, Alizah, were giving immunization drops to children on January 18 when two gunmen riding on a motorcycle shot them.
No one has so far claimed responsibility for the attack, but militants in Pakistan have regularly targeted polio workers and their guards.
Another police official said the mother and the daughter were 38 and 16, respectively.
Militants say the polio vaccination campaigns are a cover for Western spies or a conspiracy to sterilize Pakistani children.
Prime Minister Shahid Khaqan Abbasi condemned the latest attack and ordered an investigation.
"Polio teams are rendering a huge national service to save our children from the crippling disease," his office said in a statement. "Attack on these dedicated workers, risking their lives for their nation, is an attack on our future."
Balochistan's regional chief minister, Mir Abdul Qudus Bizenjo, called the shooting an act of "cowardice and terrorism."
"An attack on those working to serve the people is an attack on humanity," he also said.
Pakistan this week launched a drive against polio across the country.
It is one of only two countries in the world, along with neighboring Afghanistan, where polio is endemic.
The infectious disease, caused by a virus, mainly affects children under 5 years of age. It can lead to irreversible paralysis and death.
In a separate attack in Quetta, the capital of Balochistan Province, unidentified gunmen on January 18 killed two police officers on patrol.
No group immediately claimed responsibility.
Resource-rich Balochistan, which borders Afghanistan and Iran, has been plagued by sectarian violence, Islamist militant attacks, and a separatist insurgency that has led to thousands of casualties since 2004.