The United Nations' Yugoslav war crimes tribunal has ordered an independent review into its "internal operations" around the dramatic death of a Croat ex-general who swallowed what he said was poison in the courtroom and later died.

The International Criminal Tribunal for the former Yugoslavia said its review will complement a investigation by Dutch prosecutors into Slobodan Praljak's death on Wednesday.

The announcement came after Croatia's justice minister called into question the speed of responses by security and medical staff after Praljak, the 72-year-old former commander of Bosnian Croat military forces, shouted that he was innocent and then raised his trembling right hand to his lips and drank from a small bottle.

It came seconds after an appeal judge had confirmed much of Praljak's conviction and his 20-year sentence for war crimes and crimes against humanity during the 1992-95 Bosnian war.

Dutch prosecutors have confirmed the bottle contained a toxic chemical, but have not identified the liquid. It remains unclear how Praljak got the bottle and managed to smuggle it into the courtroom.

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 December 31 when the tribunal formally closes its doors for the last time, having completed all its cases.

The court said Mr 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".

The Netherlands Forensic Institute said it will conduct a post-mortem on Praljak's body, but it is not clear when that will happen.

Croatia's justice minister Drazen Bosnjakovic said the country will ask Dutch authorities to be included in the investigation into Praljak's death.

Mr Bosnjakovic told Croatian state TV: "Much remains unclear, including how the poison was taken in, why security didn't react in time and why medical help arrived so late."

He added that Croatia wants "all facts cleared about this tragic event".

Speaking on Thursday at Zagreb airport, Praljak's lawyer Nika Pinter told Croatia's Nova TV she did not know how he managed to get the bottle past security.

"But that was his decision, his decision," Ms Pinter said. "He would not want to live for one day with handcuffs on his hands, and (the) stigma of war criminal on his back.