Serbian war crimes suspect Goran Hadzic went before a UN war crimes tribunal on Monday, the HRT Croatian national TV channel reported.
He appeared before South Korean Judge O-Gon Kwon at the International Criminal Tribunal for the former Yugoslavia (ICTY) in The Hague.
He was asked to identify himself and his rights were read.
If Hadzic fails to enter a plea, a "not guilty" plea will be entered on his behalf. If he pleads guilty, no trial will take place and he will be sentenced.
Hadzic, 52, was extradited to The Hague on Friday for his role in the 1991-95 Croatian war.
Hadzic was the ICTY's most wanted suspect after the arrests of former Bosnian Serb president Radovan Karadzic in 2008 and former Bosnian Serb army chief Ratko Mladic earlier this year.
The ICTY has charged him with 14 counts of crimes against humanity and war crimes including the extermination, murder and willful killing of hundreds of Croat and non-Serb civilians.
Hadzic was arrested after seven years on the run after being discovered by Serbian agents in the Fruska Gora region, north of Belgrade, not far from his family home.
Serbian media are speculating over where and how Hadzic has been since he went on the run after indictment by the ICTY.
Some suggested he had been abroad, citing Russia, Belarus and Romania as possible states he could have hidden out in.
