Mohammed Abdel Hafiz Busafa, assistant director at the hospital, said the patient was under anesthetic and was being treated for an infected gunshot wound when gunmen entered the operating room.
The gunmen threatened the doctors and took the patient from the hospital and killed him. The patient's body was found on the steps of a nearby building, the Libya Herald reported Monday.
Busafa said the incident caused "shock and bewilderment," and medical staff were in a state of fear. He said the killing was an attack on patients' rights.
Staff at the hospital were referring patients elsewhere for treatment, the Herald said.
Sebha is in southwest Libya.