Three US doctors were killed and one person injured Thursday when an Afghan policeman opened fire on them at a hospital in Kabul, dpa quoted a government official as saying. "A policeman who was a guard at the Cure Hospital fired on some foreigners this morning," Interior Ministry spokesman Sediq Sediqqi said. "The attacker was injured as well. He is now in police custody and we are investigating," Sediqqi said. He said the three fatalities were doctors at a hospital, which is child care specialized and run by a US charity, and funded by USAID.