Prosecutors in the Netherlands say an autopsy on a former Croatian general who died after swallowing a liquid at a war crimes hearing showed he had cyanide in his system. 

The Hague public prosecutor's office said in a statement Friday night that preliminary results from a toxicological test revealed "a concentration of potassium cyanide" in Slobodan Praljak's blood. 

The cyanide caused heart failure that the statement described as the 72-year-old Praljak's "suspected cause of death."

Praljak drank from a small bottle seconds after an appeals judge at the International Criminal Tribunal for the former Yugoslavia confirmed his 20-year sentence for crimes during the 1992-95 Bosnian war.

Two Croatian experts observed the autopsy at the tribunal's request.

UN orders review

Meanwhile, the United Nations tribunal ordered an independent review of its "internal operations" following the dramatic event in its courtroom. The tribunal said its review was meant to complement the ongoing investigation of Praljak's death by Dutch prosecutors. 

The announcement came after Croatia's justice minister raised doubts about whether security and medical staff at the tribunal responded quickly enough when Praljak raised the bottle to his lips with a trembling right hand and consumed its contents. 

Before the toxicological test results came back, Dutch prosecutors had confirmed the bottle carried a toxic chemical. It remains unclear how Praljak, who was in custody before the hearing, obtained the substance and managed to smuggle it into the courtroom.

Former Bosnian war veteran drinks apparent poison at his criminal trial0:28

Cyanide is a fast-acting chemical that can be deadly in different forms. Cyanide gas is considered the most harmful, but swallowing cyanide can also be lethal. 

Potassium cyanide, found in Praljak's blood, is a white powder that can have a bitter, almond-like odour. Cyanide kills by preventing the cells of the body from using oxygen, and is particularly harmful to the heart and brain, according to the U.S. Centers for Disease Control and Prevention.

The tribunal's review will begin next week and be led by Hassan Jallow, a former prosecutor with the UN's Rwanda war crimes tribunal. It aims to file a report by Dec. 31, when the tribunal formally closes its doors, having completed all its cases. 

The court said Jallow "is mandated to undertake an assessment of relevant existing procedures as well as make any recommendations which may assist other courts in the future."