An Afghan security guard shot and killed three Americans at a hospital in Kabul on Thursday. Officials said the three killed were doctors, including a visiting father and son.
Another doctor and a U.S. nurse were wounded in the attack.
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 at Cure International Hospital and started shooting.
"Five doctors had entered the compound of the hospital and were walking toward the building when the guard opened fire on them," said Kanishka Bektash Torkystani, a Ministry of Health spokesman. "Three foreign doctors were killed."
The identities of the victims were not released. The U.S. Embassy in Kabul confirmed that three Americans were killed but did not give any further information.
Two of the dead were a visiting father and son, Minister of Health Soraya Dalil said, adding that the other victim was a Cure International doctor who had worked for seven years in Kabul.
The gunman was wounded and in custody. He was in surgery at midday in the same medical facility under heavy police guard, according to Torkystani.
The attack at the Cure International Hospital, which specializes in child and maternity health, is the latest incident in which Afghan security forces have targeted foreigners. Cure is a non-profit organization that operates in 29 countries.
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.
Afghanistan held a presidential election on April 5 with preliminary results due to be released this weekend.