Former Serbian spy chiefs Jovica Stanisic and Franko Simatovic were convicted in 2021
Former Serbian spy chiefs Jovica Stanisic and Franko Simatovic were convicted in 2021 AFP

Two of late Serbian president Slobodan Milosevic's spy chiefs face an appeals judgment Wednesday in the final Hague war crimes trial from the 1990s Bosnian conflict.

Former state security service boss Jovica Stanisic, 72, and his deputy Franko Simatovic, 73, were jailed by a UN court for 12 years in June 2021.

They were convicted of backing a Serb death squad that terrorised the Bosnian town of Bosanski Samac in 1992 with killings, rapes and looting.

Stanisic and Simatovic have both challenged their convictions for the war crime of murder and the crimes against humanity of murder, persecution, forcible transfer and deportation.

Prosecutors have appealed against the pair's acquittal on several other charges, and asked for a longer sentence.

The case has been running for two decades, making it the longest and the last at the UN tribunal dealing with crimes from the wars that tore apart Yugoslavia after the fall of communism.

They were cleared at an initial trial in 2013 but the court ordered a retrial.

A five-judge panel at the court, known as the International Residual Mechanism for Criminal Tribunals (MICT), will hand down its appeal judgment from 11:00am (0900 GMT) Wednesday, it said in a statement.

The MICT has taken over cases left over from the International Criminal Tribunal for the former Yugoslavia (ICTY), which closed in 2017 after bringing key suspects to justice over the Balkans wars.

Suspects including Bosnian Serb political leader Radovan Karadzic and military chief Ratko Mladic have previously been convicted by the original international court, while Milosevic himself died in custody in The Hague in 2006.

But the case of Stanisic and Simatovic has dragged on far longer.

The two spymasters were arrested in 2003 and acquitted in 2013 after a five-year trial, but the ICTY ordered a retrial in 2015 after a public outcry.

Judges in 2021 convicted the pair of helping train and deploy Serb forces during the takeover of Bosanski Samac in April 1992.

Serb forces launched a "campaign of terror" to drive out non-Serbs involving rapes, looting and the destruction of religious buildings in the town, judges said.

They also held Bosnian Muslims and Croats in six detention centres were they were subjected to forced labour, repeated beatings, torture, and sometimes killings.

But judges said there was not enough evidence to prove prosecution claims that Stanisic and Simatovic were part of a concerted plot led by Milosevic to drive out Croats and Bosnian Muslims and create a Serb homeland.

Lawyers for the defendants say the 2021 judgment failed to show that the pair exerted any control over the Serb forces that brutalised Bosanski Samac.

The Balkans wars left about 130,000 people dead and millions displaced.

Tensions continue to simmer in the region, with clashes erupting on Monday in northern Kosovo between ethnic Serbs and NATO-led peacekeepers.

Former Kosovan president Hashim Thaci is currently on trial for war crimes at a separate tribunal in The Hague.