JOHANNESBURG – South Africa's former President Nelson Mandela underwent a successful surgery to remove gallstones Saturday, the nation's presidency said, as the 94-year-old anti-apartheid icon is still recovering from a lung infection.

Doctors treating Mandela waited to perform the endoscopic surgery as they wanted to first attend to his lung ailment, presidential spokesman Mac Maharaj said in a statement. Mandela has been hospitalized since Dec. 8.

In the procedure, a patient usually receives sedatives and an anesthetic to allow a surgeon to put an endoscope down their throat, authorities say. The surgeon then can remove the gallstones, which are small, crystal-like masses that can cause a person tremendous pain.