Former Yugoslav President Slobodan Milosevic has died in the detention centre at The Hague tribunal.
The tribunal said he was found dead in his cell on Saturday morning and that although the cause was not yet clear, there was no indication of suicide.
Mr Milosevic, 64, had been on trial at the UN war crimes tribunal for genocide and other war crimes since 2001.
A full autopsy will now be carried out on Mr Milosevic, who had high blood pressure and a heart condition.
Last month the tribunal rejected a request by the former president to go to Russia for medical treatment, despite the Russian government saying it would ensure he returned to The Hague to continue his trial.
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His death affected me only because he didn't pay his debts to Serbs and others that suffered after his foolish actions
Radosh, Belgrade, Serbia
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Milosevic dead: reaction
UK reaction to death
"Russian doctors were prepared to give him the necessary aid and the Russian authorities guaranteed to meet all the demands of the International Criminal Tribunal for the former Yugoslavia," a spokesman from Russia's foreign ministry said on Saturday.
"Unfortunately, in spite of our guarantees, the tribunal did not agree to give Slobodan Milosevic the possibility of being treated in Russia," he added.
Damage to tribunal
The tribunal has ordered an inquiry into the death.
"Milosevic was found lifeless on his bed in his cell at the United Nations detention unit," the tribunal said in a statement.
He was determined to continue fighting his case
Milosevic lawyer, Steven Kay QC
Milosevic's lawyer speaks
Tribunal statement on death
"The guard immediately alerted the detention unit officer in command and the medical officer. The latter confirmed that Slobodan Milosevic was dead."
The BBC's Geraldine Coughlan at The Hague says Mr Milosevic's death is a blow to prosecutors, who had been hoping to convict him as being part of a joint criminal enterprise that operated across the former Yugoslavia, intent on setting up a greater Serbian state.
Mr Milosevic faced charges of war crimes and crimes against humanity for his alleged central role in the wars in Bosnia, Croatia and Kosovo during the 1990s.
He also faced genocide charges over the 1992-95 Bosnia war, in which 200,000 people died.
'Punished already'
Mr Milosevic was in office for 13 years until 2000.
European Union foreign policy chief Javier Solana said he hoped his death would help Serbia to come to terms with its past and allow it to look to the future.
Full war crimes charges
Mothers and widows of Muslims killed in Srebrenica during the Bosnian war said they regretted that Mr Milosevic's death meant he would never face justice for the killings.
"However, it seems that God punished him already," said Hajra Catic of the Association of Srebrenica mothers.
Serbia-Montenegro's Foreign Minister Vuk Draskovic, who accused Mr Milosevic of organising the assassinations of many of his colleagues and family, said it was a pity the former president had not faced justice in Belgrade.
Second death
Mr Milosevic's brother Borislav was quoted by Interfax news agency as saying the war crimes court was "entirely responsible" for his death.
The former president had been ill for some time, and his trial was interrupted last year because of health problems.
His lawyer told BBC News 24 that Mr Milosevic would not have committed suicide because he wanted to complete his trial, which had been due to restart on 14th March and was scheduled to end in May this year.
"In fact he said to me a few weeks ago. 'I hadn't fought this case for as long as I have with any intention of to do any harm to myself, Mr Kay'. And that is why he wanted medical treatment," Steven Kay said.
Both the former Serbian leader's parents committed suicide.
Mr Milosevic's death comes just six days after a fellow Serb prisoner at The Hague, Milan Babic, committed suicide.
The Croatian Serb leader had pleaded guilty to crimes against humanity carried out during the 1991-95 war in Croatia.
Both my parents are from Macedonia.
The Former Yugoslav republic. Just thought id add it...
wow :o
an australian of macedonian descent
im an american of french descent