A convicted Croat war criminal reportedly died on Tuesday after apparently drinking poison when a United Nations judge upheld a 20-year sentence handed down for his involvement in war crimes against Bosnian Muslims in the 1990s.

Reuters, citing Croatian state television, reported that Bosnian Croat commander Slobodan Praljak died shortly after appearing to ingest a small bottle of what he claimed was poison. The broadcaster quoted people close to Praljak as saying that he died in a hospital in the Hague shortly after drinking the substance.

Praljak was convicted by the International Criminal Tribunal for the Former Yugoslavia in 2013 of war crimes stemming from his involvement in a campaign to rid a would-be Bosnian Croat mini-state of Muslims during the Croat-Bosnian War.

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In its final verdict before it is dissolved next month, the U.N. tribunal upheld the convictions of six Bosnian Croats found guilty of war crimes and crimes against humanity during the Bosnian War.

The judge presiding over Praljak's appeal overturned some of the convictions, but upheld others and confirmed the 20-year sentence previously handed down to him.

According to Reuters, after the judge upheld the sentence, Praljak drank from the bottle and announced that he had just ingested poison.

"I am not a war criminal," he said. "I oppose this conviction.”

The judge then suspended the hearing and declared that the courtroom had become a "crime scene," The Associated Press reported.