Slobodan Praljak, a Bosnian Croat war criminal, has died in hospital after drinking poison during an appeal hearing before the International Criminal Tribunal for the former Yugoslavia (ICTY) in The Hague on Wednesday.

The 72-year-old drank from a tiny bottle after his 20-year prison sentence was upheld by the court. He was immediately rushed to a hospital where he died.

In 2013, Praljak was sentenced for crimes in the city of Mostar during the Bosnian war of 1992 to 95.

He was one of six former Bosnian Croat political and military leaders who are standing trial before the ICTY.

After hearing the verdict, Praljak said he rejected the ruling, insisting that he was not a war criminal.

“Slobodan Praljak is not a war a criminal, I am rejecting the court ruling,” he said, before raising his hand to his mouth and swallowing some liquid from a tiny glass bottle.

“I have taken poison,” he said.

At that, Carmel Agius, the presiding Judge, immediately suspended the proceedings and an ambulance was called.

“We suspend the… We suspend… Please, the curtains. Don’t take away the glass that he used when he drank something,” Agius said.

The UN court subsequently announced that the courtroom was now “a crime scene”.

An ambulance was later seen arriving outside the tribunal while several emergency rescue workers also rushed into the building carrying equipment in backpacks.

In a statement, the ICTY said Praljak “was immediately assisted by the ICTY medical staff” and was “transported to a nearby hospital to receive further medical assistance where he passed”.

An independent investigation is now underway.

Commenting on the incident, Andrej Plenkovic, Croatia’s Prime Minister, said Praljak’s death was regrettable.

“His act, which we all unfortunately witnessed today, speaks most of a deep moral injustice towards six indicted Croats from Bosnia and the Croatian people,” Plenkovic said.

“The government expresses its condolences to all victims of all crimes committed in the war in Bosnia-Herzegovina. We voice dissatisfaction and regret about the verdict.”

Praljak, a former Commander of the Main Staff of the Bosnian Croat defence forces (HVO), was jailed for crimes against humanity.

The court ruled that Praljak was aware that soldiers were rounding up Muslims in Prozor in the summer of 1993, but he failed to make any serious efforts to stop the action.

Those appearing with him included Jadranko Prlic, the former Prime Minister of the Bosnian Croats’ breakaway statelet.

The ICTY was set up by mandate of the UN Security Council in 1993, and is due to close when its mandate expires at the end of the year.