Karadzic was convicted two years ago for some of the worst war crimes committed as the former Yugoslavia broke apart in the 1990s, including the 1995 Srebrenica massacre in which around 8,000 Bosnian Muslim men and boys were killed.

"We are here today to ask you to overturn Radovan Karadzic's conviction and order a new trial," defence lawyer Peter Robinson told a panel of United Nations judges on Monday as two days of appeal hearings got underway.

In the courtroom a group of victims from the 'Bosnian Mothers of Srebrenica' organisation watched Karadzic, 72, who looked healthy and resolute in a grey suit and red tie. He was seated behind his legal team.

Karadzic, who was arrested a decade ago after a years-long manhunt, was found guilty on 10 counts of genocide, war crimes and crimes against humanity for the brutal campaign of ethnic cleansing in Bosnia that he oversaw as president of the breakaway Bosnian Serb Republic.

But his lawyer described the initial seven-year trial as "unwieldy" and as an "out-of-control mega-trial" which they said violated his rights to a fair hearing.

Later on Monday, Karadzic will take the floor to argue that the initial judgement was wrong in concluding that he was a member of an overarching joint criminal enterprise to drive out non-Serbs from Serb-claimed territory in Bosnia and Croatia.

He also intends to contest the charge that he supported the shelling of civilians during the 44-month siege of Sarajevo, his lawyer told the court.

Karadzic's conviction was handed down by UN judges at the International Criminal Tribunal for the former Yugoslavia (ICTY) which said he was "at the apex of power" of the Bosnian Serb military and political hierarchy when atrocities were committed by his troops.

The appeals hearing is being held at the International Residual Mechanism for Criminal Tribunals (MICT), which is handling outstanding UN war crimes cases for the Balkans and Rwanda.

Australian Associated Press