A UN court has denied a bid by convicted Bosnian Serb war criminal Ratko Mladić to be released from jail on the grounds he is near the end of his life.

While agreeing that he was "in the final stages of his life", Judge Graciela Gatti Santana said conditions at the UN prison and its hospital in The Hague "are of such high quality that Mladić comfort can be maximally ensured".

"There is no additional treatment available elsewhere that is unavailable in the Netherlands."

Mladic, 84, was jailed for life in 2017 for genocide, war crimes and crimes against humanity during the wars in ex-Yugoslavia in 1992-95. The sentence for the man known as the "Butcher of Bosnia" was upheld on appeal in 2021.

In a written ruling on Thursday, Judge Gatti Santana admitted that "Mladić's current situation is dire."

But she added he "continues to receive comprehensive and compassionate treatment" from qualified doctors, nurses and prison staff.

"He benefits from an exceptional visitation regime, which allows for frequent contact with his friends and family, including the possibility of family members to be present with him during his final moments," the ruling said.

It was not immediately clear whether Mladić would be able to appeal against the decision.

But they said he had then suffered a suspected stroke during a call with his son that left him almost unable to speak.

They said two doctors had assessed his condition as serious and the "risk of imminent death is high", calling for his immediate provisional or conditional release to a hospital or hospice where the Serbian language is spoken.

It was implicit that the defence team had been seeking his return home, with Serbia's government making it clear it would be prepared to provide guarantees to the court if they released him.

Mladic commanded Bosnian Serb forces in the 1990s against the Bosnian Croat and Bosniak (Bosnian Muslim) armies, during a war in which his troops committed "ethnic cleansing" in Bosnia-Herzegovina, besieged the main city of Sarajevo with the deaths of more than 10,000 people, and carried out the massacre of 8,000 men and boys at Srebrenica.

More than 100,000 people were killed and about two million displaced during the Bosnian war.

Mladic disappeared in 1995 and was only tracked down in rural Serbia in 2011 after 16 years on the run. He went on trial at The Hague in 2012 and was convicted in 2017.

Bosnian groups representing victims and survivors strongly oppose the former Bosnian Serb commander's release from jail, describing it as a "legal tactic" rather than a humanitarian request.