Former Yugoslav President Slobodan Milosevic died of heart failure, according to a preliminary autopsy.
The UN War Crimes Tribunal have released a statement saying he died of a heart attack.
However, poisoning cannot yet be ruled out in relation to his death, a spokesperson for the tribunal admitted.
Mr Milosevic's remains will be released to his family tomorrow.
The reason for the heart failure was not given and the tribunal said a toxicology report will still be carried out.
Mr Milosevic had suffered from high blood pressure and a heart condition and his poor health repeatedly interrupted his trial.
He has been blamed for the deaths of hundreds of thousands of people in Bosnia, Croatia and Kosovo, during the disintegration of Yugoslavia in the 1990s.
He appears to have died of natural causes, but his lawyer said the post mortem should have taken place elsewhere as his client had believed he was being poisoned in the jail.
In Serbia, there has been a muted reaction to the death. A handful of supporters gathered in Belgrade for a memorial service in the early hours of this morning.
The Serbian Prime Minister, Vojislav Kostunica, offered his condolences to Mr Milosevic's family and party but said this was not the time to say anything more.
The Serbian Foreign Minister, Vuk Draskovic, expressed regret that the ousted leader did not live to be sentenced.
The United States said the former leader had been responsible for the violent dismemberment of Yugoslavia.
