An Afghan security guard working for the Interior Ministry opened fire on American doctors in a Kabul hospital today, killing three and wounding an American nurse.

The hospital, affiliated with Christian charity Cure International, was established in 2005, and specializes in pediatrics. Dr. Jerry Umanos, a pediatrician from Chicago, had been working there since many years. The two other doctors, identified as a father and son, were visiting the site.

What prompted the shooting remains unclear, but the attacker was wounded during the incident and underwent surgery in the same hospital. He is recovering and will be questioned soon.

The US embassy confirmed the incident, but offered no further details. So far no group has claimed responsibility for encouraging the shooting, either.