Summary:
A police officer has been shot dead by gunmen who tried to ram a team carrying out polio vaccinations in Pakistan, officials say.

Full article:
(CNN) -- Two gunmen opened fire Thursday on a team carrying out polio vaccinations in Pakistan's southwestern Balochistan province, killing the police officer guarding them. "The assailants sped away on their motorcycle after the attack," Shah Muhammad, a police official, told CNN. There was no immediate claim of responsibility for the attack, which occurred in Balochistan's Loralai district. A police investigation was under way. Teams carrying out polio vaccinations in Quetta, Pishin, Loralai and other parts of Balochistan have been repeatedly attacked by militants. CNN's Marie-Louise Gumuchian contributed to this report.