4 polio workers killed in Pakistan

Four members of a polio vaccination team were killed in an attack by militants in western Pakistan's Balochistan province on Wednesday, police said.

Attackers on two motorcycles opened fire at the team in the eastern part of Quetta, the capital of Balochistan province. Two polio workers were killed during the attack, and the two others who were injured died later at a hospital, said Imran Qureshi, a senior police officer.

There was no immediate claim of responsibility.

The province's chief minister, Malik Baloch, vowed to protect polio vaccination teams and bring the attackers to justice.

"We will not bow down before terrorists," Baloch said.

Anti-polio campaigns have been targeted by militants in Pakistan since U.S. intelligence officials used a vaccination program to help in their hunt for Osama bin Laden in 2011. Under cover of the program, the CIA sought to collect DNA samples from relatives of the al Qaeda leader to verify his presence in a compound in Abbottabad.

Balochistan's government launched a polio vaccination campaign after a rise in polio cases. Fourteen polio cases have been reported this year in the province.