Prosecutors are set to explain to United Nations judges why they believe that the 2016 acquittal of a Serbian ultranationalist on war crimes and crimes against humanity charges should be overturned on appeal.

Serbian lawmaker Vojislav Seselj, who was found not guilty of all nine charges against him at the International Criminal Tribunal for the former Yugoslavia, has vowed not to attend Wednesday's hearing in The Hague.

At trial, prosecutors accused him of crimes including persecution, murder and torture and demanded a 28-year sentence for his support of Serb paramilitaries during the region's bitter, bloody wars in the early 1990s.

But judges acquitted him in a controversial majority decision, saying there was insufficient evidence. One of the three judges dissented, saying the acquittals ignored international law and the tribunal's jurisprudence.