Unidentified gunmen opened fire at a van carrying polio workers in Mengalabad adjacent to Eastern Bypass of Quetta.
Four polio workers were killed in the attack and two others were injured in the firing incident, police sources said.
Pakistan is one of three countries in the world where the polio virus is endemic. The other two countries are Afghanistan and Nigeria.
The government’s efforts to free the country from the crippling disease have been fiercely resisted by the militants. The vaccination teams have suffered repeated attacks and score of the health workers were killed in these attacks.