Updated

Portuguese authorities say Mile Mrksic, a former Serb army officer sentenced by a U.N. tribunal to 20 years in prison for his part in the 1991 torture and killings of nearly 200 Croatians during the Balkan wars, has died. He was 68.

The Portuguese Prison Services Directorate, which oversaw his incarceration at a high-security prison in Lisbon, said Monday that Mrksic died at a public hospital Aug. 16 from a "progressive and irreversible" disease. It provided no further details.

Mrksic surrendered to the U.N. Yugoslav war crimes tribunal in 2002. He was convicted in 2009 of withdrawing troops who were guarding Croatian prisoners of war, thereby allowing paramilitary forces to massacre them. The court found he also failed to prevent torture and cruel treatment in the atrocity.