Though allies against the Bosnian Serbs in the war, Bosnian Croats and Muslims also fought each other for a period of 11 months, with Mostar seeing some of the fiercest fighting.
Slobodan Praljak brings a bottle to his lips, during a Yugoslav War Crimes Tribunal in The Hague, Netherlands.
War criminal Slobodan Praljak has died after "drinking poison" as judges upheld his 20-year prison sentence at the Hague, according to Croatian state TV.
"My client says he drank poison this morning", defence attorney Natasa Faveau-Ivanovic said.
Croatian Prime Minister Andrej Plenkovic later confirmed that Praljak had died, saying in a government tweet, "On behalf of the Government of the Republic of Croatia and on my own behalf, I want to express my deepest condolences to the family of General Slobodan Praljak".
The courtroom where the dramatic scene unfolded was sealed off and Presiding Judge Carmel Agius said that it was now a "crime scene" so that Dutch police could investigate. Praljak was taken away from the court by an ambulance.
Some of his convictions for actions in the later years of the conflict were overturned, but his sentence was not.
The Yugoslavia tribunal, created in 1993 by the United Nations Security Council, has prosecuted hundreds of people for war crimes and is scheduled to shut down at the end of this year.
The judges were ruling in the appeals of six former Bosnian Croat political and military leaders accused in a campaign against Bosnian Muslims during the breakup of Yugoslavia.