Former Bosnian Serb political leader Radovan Karadzic was sentenced to life in prison after a UN court rejected his appeal and increased his original sentence of 40 years behind bars.

Karadzic was found guilty of genocide, crimes against humanity and war crimes by a UN tribunal in The Hague in 2016 and was handed a 40-year jail sentence.

But after hearing his appeal, in which he claimed that the persecution and expulsion of Croats and Muslims was a myth, the UN court ruled that the original sentence was too light and increased it to life.

Vagn Joensen, the presiding judge, said a heavier sentence was justified, given the "sheer scale and systematic cruelty" of the crimes perpetrated by Karadzic, a former psychiatrist who became the president of the Bosnian Serb breakaway state, Republika Srpska.

The original sentence underestimated “the extraordinary gravity of Karadzic's responsibility and his integral participation in the most egregious of crimes,” he said.

Karadzic orchestrated the 1995 Srebrenica massacre, in which Bosnian Serb soldiers killed nearly 8,000 Muslim men and boys in what was supposed to be a "safe area" protected by Dutch peacekeeping forces. It was the worst atrocity in Europe since the end of the Second World War.