Two policemen guarding a team of anti-polio vaccinators were gunned down in southwestern Pakistan on Tuesday, the Interior Ministry said.
The incident -- the latest in a series of similar attacks -- occured in the remote Naushki district of southwestern Balochistan province.
The vaccinators were unhurt in the attack.
No group has claimed responsibility for the attack, although militants loyal to the Tehreek-e-Taliban Pakistan have long been targeting anti-polio vaccinators across the country.
The latest attack coincides with a fresh countrywide anti-polio campaign to vaccinate millions of children under age 5.
Interior Minister Mohsin Naqvi condemned the incident, directing the law enforcement agencies to use "all available resources" to bring the perpetrators to justice.
Pakistan is among the only two countries, including Afghanistan, in the world where polio is endemic.
The South Asian country has reported four confirmed polio cases this year.
