A Pakistani police spokesman says gunmen have killed four health workers administering polio vaccines in a southwestern city.
Shahzada Farhat says those killed in the Wednesday attack in Quetta included three women.
He says the vaccination team of three women and three men was waiting for a police escort when the two gunmen opened fire on them.
Local militants oppose the vaccination campaign, alleging that western governments would use it as a cover to spy on insurgents.
Pakistan is one of only three countries in the world where polio, which can cause paralysis and death, remains endemic.