Lawyers defending Bosnian Serb ex-army chief Ratko Mladic on Thursday asked Yugoslavia war crimes court judges to extend a delay in his trial by six months, ahead of testimony by its first witness.

Lawyer Branko Lukic, in a submission to the International Criminal Tribunal for the former Yugoslavia "respectfully requests that the trial chamber... enter an order continuing the start of presentation of evidence an additional six months," the court said.

His request comes after judges adjourned Mladic's genocide, war crimes and crimes against humanity trial a day after it opened in The Hague on 16 May, due to "irregularities" in the transfer of prosecution documents to the defence to enable it to prepare for the trial.

Judges later set down 25 June as the date for the former general's trial to resume with the testimony of the prosecution's first witness, originally scheduled for 29 May.

Mladic, 70, the so-called "Butcher of Bosnia", is charged with 11 counts of war crimes, crimes against humanity and genocide committed during Bosnia's 1992-1995 war.

They include in particular the masterminding of the July 1995 Srebrenica massacre of almost 8,000 Muslim men and boys, the worst atrocity on European soil since World War II.

Prosecutors also hold Mladic responsible for the 44-month siege of Sarajevo that left an estimated 10,000 people dead, the vast majority of them civilians.

Mladic, who was arrested a year ago in Serbia after more than 16 years on run, pleaded not guilty to the charges at an earlier court hearing. He faces life imprisonment if convicted.