The session was meant to mark the final act of a 24-year legal process over the atrocities of the Bosnian war. Instead, it descended into chaos and confusion.

Judges at the International Criminal Tribunal for the Former Yugoslavia were in the midst of delivering appeals rulings on Wednesday involving six defendants over Croatia’s often-overlooked involvement in the conflict. They upheld two of the sentences before moving on to Slobodan Praljak, who had been sentenced to 20 years in prison for war crimes linked to his involvement in an offensive against a Bosnian town.

But when judges announced that they had upheld the sentence against Mr. Praljak, he addressed the bench in Croat, raised a small vial and drank from it. His lawyer cried out, “Your honors, my client says he has taken poison,” and Mr. Praljak was taken from the courtroom shortly afterward. The hearing was suspended, and rulings on the remaining three appeals have yet to be announced.

Dutch police officers and an ambulance rushed to the tribunal, seated in The Hague, but no immediate report on Mr. Praljak’s condition was available.

The case draws attention to Croatia’s often-overlooked role in the Bosnian war.

The tribunal has for the past 24 years largely focused on the dominant Serbian role in the conflict, most recently sentencing Ratko Mladic, the former Bosnian Serb military commander, to life in prison for genocide, crimes against humanity and war crimes.

But Croatia, a range of trials at the tribunal have shown, also orchestrated a brutal ethnic cleansing campaign to seize Bosnian lands once the Yugoslav federation began to disintegrate in 1991.

Indeed, both Croatia and Serbia set out to redraw international borders by forcibly moving swathes of people and creating homogeneous zones out of Bosnia, which until then had been a small Yugoslav republic in which ethnic groups were thoroughly mixed. Trials have demonstrated that the ethnic cleansing that took place was not a side-effect of warfare, but the goal of both the Serbian and Croatian governments.

The two countries’ leaders, Slobodan Milosevic of Serbia and Franjo Tudjman of Croatia, held secret talks early in 1991 to divide up Bosnia. Mr. Mladic, court records showed, had at least two subsequent meetings with Croat counterparts.

Forces led by Mr. Mladic moved first, in 1992. But the following year, Mr. Tudjman’s campaign to occupy lands that he claimed were historically Croat kicked into gear. It used militia forces to terrorize people and force them to flee, tactics similar to Mr. Mladic’s, though there was less coldblooded killing, and the number of prisoners and refugees was smaller.

“President Tudjman believed that Bosnia and Herzegovina would not, and should not, continue as a sovereign independent state,” Peter Galbraith, the former United States ambassador to Croatia, said in testimony to the tribunal. Mr. Tudjman died in 1999, before the tribunal had completed his indictment.

Prosecutors said militias that were funded and staffed by the Croatian government, and following its orders, set about rounding up non-Croatian men, imprisoning up to 10,000. Women and the elderly were abused, raped and at times killed. Tens of thousands fled. Most of the victims were Bosnian Muslims, known as Bosniaks, but Serbs and Roma people also suffered.

Though none of the trials involving Croatia were on the scale of the killings carried out by Bosnian Serb forces in Srebrenica or Sarajevo, a dozen ethnic Croats have been convicted by the tribunal for crimes related to their campaign of violence. The most widely publicized Croatian military action was the monthslong siege and shelling of the ethnically mixed city of Mostar, including the destruction of its centuries-old stone bridge.

The case being heard on Wednesday was an appeal involving six Croats sentenced to prison terms of between 10 years and 25 years for their role as military or political leaders during the Bosnian campaign. Mr. Praljak, 72, was convicted of war crimes over the Mostar offensive.

Both the prosecution and the defense had brought appeals against the judgments handed down against the men.

Prosecutors had sought longer sentences, and affirmation from the tribunal that the Croatian government funded and controlled the militias inside Bosnia, following direct orders from Mr. Tudjman.

They offered evidence including extensive records kept by Mr. Tudjman of his conversations, meetings and telephone calls, released to prosecutors after his death. They also presented documents showing that his government sent funds, vehicles, weapons and senior military commanders to run the operations in Bosnia. After Mr. Tudjman’s death, the tribunal also received transcripts and archives covering crucial periods of the war.

The defense sought the release of the accused, or reductions in their sentences.

But the main objective of the Croatian government appeared to be to clear the name of Mr. Tudjman, his defense minister, Gojko Susak, and the head of the army at the time, Janko Bobetko. Croatian authorities have argued the three, who have all since died, played no role in the Bosnian violence and were not, as an earlier judgment found, part of a “joint criminal enterprise.”

The timing of the latest ruling was unrelated to last week’s sentencing of Mr. Mladic. But the pair of decisions mark a historic moment for the tribunal, with the Croatia judgment planned to be its final act before it closes at the end of the year. It was established by the United Nations Security Council in 1993 in response to the atrocities. A small appellate court will handle pending appeals, and the retrial of Serbia’s former intelligence chiefs.