CURE International has expressed its "deep sadness" over the fatal shooting of three American doctors at its hospital in Kabul.
Dr Jerry Umanos, a paediatrician from Chicago, had served at the hospital in Afghanistan for more than seven years.
The other two victims have not yet been named but were reported by Minister of Health and Soraya Dalil to be an American father and son.
CURE said the two were not employees of the charity but guests visiting the hospital when the shooting occurred on Thursday morning.
The shooter was also not an employee of CURE but a member of the Afghan police detail assigned to protect the hospital.
According to CURE, the assailant shot himself after the attack and was taken into surgery by the hospital staff before being transferred into the custody of the Afghan government.
"We don't know yet the motivation of the assailant and are still working very closely with the Afghan authorities to learn all the details surrounding this tragic incident," said CURE chief executive Dale Brantner in a statement.
He paid tribute to Dr Umanos and his faithful service in "caring for the most vulnerable members of society - children and premature infants - and helping them survive the harsh realities of childbirth in Afghanistan".
"We may never know the number of future doctors, teachers, or law enforcement officers who were given the chance to live full and healthy lives because of the work of the CURE International Hospital staff and the service and sacrifice of Jerry and his family," he said.
It is the first fatal incident at CURE's facilities in Afghanistan since it began operations in the country in 2002 but Mr Brantner added that the shooting "reinforces our need for vigilance" and that CURE would continue its work there.
Christians are being asked to pray for the families of the three victims as they come to terms with their loss, as well as the safety and welfare of CURE's 1,600 employees around the world.