Appeals judges upheld Karadzic's conviction for the 1995 genocide at Srebrenica and ruled that the 40-year sentence imposed at the close of his trial was too light, given the "sheer scale and systematic cruelty" of the crimes in question.

Survivors broke into applause after Presiding Judge Vagn Joensen read the sentence on Wednesday. Karadzic, who had argued that the United Nations court was biased against him, stood impassively.

The five-judge panel ruled that the 40-year sentence originally imposed on Karadzic was too light given the "extraordinary gravity" of the crimes and "their sheer scale and systematic cruelty".

"Karadzic failed to bring into dispute the first-instance verdict's conclusions about his intent to commit genocide," Joensen said, reading out the panel's decision.

Karadzic, 73, was convicted in 2016 over the July 1995 massacre of more than 8000 Muslim men and boys by Bosnian Serb separatist forces in the eastern town of Srebrenica.

He was also found guilty of leading a campaign of ethnic cleansing that drove Croats and Muslims out of Serb-claimed areas of Bosnia.

On appeal, prosecutors sought a life sentence and a second genocide conviction for his alleged role in that policy of targeting non-Serbs across several Bosnian towns in the early years of the 1992-95 war.

Judges rejected the request for the second genocide conviction, but upheld Karadzic's conviction on other war crimes and crimes against humanities charges.

Wednesday's ruling is final and cannot be challenged on appeal. It will have huge resonance in the former Yugoslavia, especially in Bosnia, where ethnic communities remain divided and Karadzic is still seen as a hero by many Bosnian Serbs.

In hiding for over a decade after the war, Karadzic was arrested and handed over to the court in July 2008.

He will remain in custody at the court's detention centre in The Hague until judges determine where he will serve out his sentence.

Australian Associated Press