Three Americans, thought to be doctors, have been shot dead at a hospital in Kabul.
District Police Chief Hafiz Khan told the Associated Press that a guard suddenly turned his weapon on the staff he was supposed to be protecting and started shooting.
"With great sadness we confirm that three Americans were killed in the attack on CURE Hospital. No other information will be released at this time," the U.S. Embassy in Kabul said, in a brief statement.
Two other people, also considered to be physicians, were reportedly wounded in Thursday's incident. No group has yet to claim responsibility.
The attack at the CURE Hospital, which specializes in child and maternity health, is the latest incident in which Afghan security forces have targeted foreigners.
In January, an attack on a popular Kabul restaurant with suicide bombers and gunmen killed more than a dozen people, while in March gunmen slipped past security at an upscale hotel in the Afghan capital and killed several diners in its restaurant.
Earlier this month, an Afghan police officer shot two Associated Press staff working in the eastern province of Khost, killing photographer Anja Niedringhaus and wounding veteran correspondent Kathy Gannon.
"We are aware of this shooting at the CURE hospital and our investigation is ongoing, but we do not know if it was carried out by our men," Zabiullah Mujahid, a Taliban spokesman, told the New York Times.