The Hague: Bosnian Croat war criminal Slobodan Praljak died after taking potassium cyanide in The Hague's courtroom, Dutch prosecutors informed, citing the results of a preliminary autopsy examination.
"This has resulted in a failure of the heart, which is indicated as the suspected cause of death," they said, BBC reported on Friday.
Praljak drank from a vial after his 20-year term for war crimes in Bosnia in the 1990s had been upheld on Wednesday.
Dutch authorities are investigating how he smuggled poison into the court.
The confirmation rulings against Praljak and five other defendants brought an end to more than 20 years of work by the International Criminal Tribunal for the former Yugoslavia (ICTY).
Seconds after hearing his appeal had been lost, the former general declared: "Slobodan Praljak is not a war criminal. I am rejecting the court ruling."
The 72-year-old then drank from a small brown-glass bottle and announced: "I have taken poison."
The presiding judge cut short the hearing and Praljak was taken to hospital.
Officials said Praljak died shortly afterwards in a local hospital.
Peter Robinson, a lawyer for convicted Bosnian Serb war criminal Radovan Karadzic, told the BBC he could not understand how anyone could have passed poison to a prisoner.
"We go through two security checks when we visit detainees," he said. "Two metal detectors. You can't bring drinks, not even a bottle of water or Coke. Everything is searched before you go in.
"I've only ever seen him (Praljak) with his family, in the room next door to us. But when his family came it was private.
"There are no guards inside the room at the time, they stay outside the door. You can see your own doctors with special permission."
Though allies against the Bosnian Serbs during the 1992-95 civil war, Bosnian Croats and Muslims also fought each other for a period of 11 months, with the city of Mostar seeing some of the fiercest fighting.
Praljak was convicted in 2013 of crimes against humanity, committed while commanding Bosnian Croat forces.