A UN court has overturned the acquittal of Serbian ultra-nationalist Vojislav Seselj for crimes committed during the 1990s Balkans conflict.

Appeal court judges in The Hague found him guilty of crimes against humanity and sentenced him to 10 years in jail.

Seselj was acquitted two years ago of nine war crimes and crimes against humanity, following a trial lasting more than eight years.

He will not return to custody as he has served 11 years in pre-trial detention.

The presiding judge Theodor Meron told the court that Seselj, a close ally of then Serbian autocratic leader Slobodan Milosevic, was guilty "of instigating persecution, deportation and other inhumane acts".

The tribunal ruled that a single speech by the academic turned far-right leader to Serb crowds in May 1992 had sparked atrocities against ethnic Croats in part of the Vojvodina province.

Seselj, Serbia's deputy prime minister between 1998 and 2000, elected to represent himself legally but refused to attend the court in The Hague.

He returned to Serbia in 2014 to undergo treatment for colon cancer.

In 2016, the International Criminal Tribunal for the former Yugoslavia acquitted Seselj of all charges against him, including murder and allegedly stoking ethnic hatred at the start of the wars that broke apart the Yugoslav federation.

While prosecutors appealed against his acquittal, Seselj was elected as a member of parliament in Serbia.

The unrepentant Serbian Radical Party leader has stuck to his nationalist line, telling news agency AFP last week he will never give up the idea of a "Greater Serbia", uniting all parts of Serbia, Bosnia and Croatia where Serbs live.

Following his acquittal in March 2016, he said: "I do not feel guilty of anything."