A lawyer representing former Bosnian Serb army chief Ratko Mladic, accused of genocide and war crimes committed during the 1992-95 Bosnian war, asked a UN court on Thursday to postpone his trial until October.

"For the defence to have any meaningful preparation, any start of the trial before October this year will be almost impossible to fulfil," his lawyer Branko Lukic told the International Criminal Tribunal for the former Yugoslavia (ICTY).

"We hope your honours will assess our position and the amount of documents, witness statements and transcripts we have received from the prosecution and those we have to gather ourselves," he said.

Judge Alphons Orie in early December said the trial against Mladic, 69, accused of 11 counts of genocide, crimes against humanity and war crimes that killed some 100,000 people, should open on March 27.

Lukic however told Orie it would take at least until October to read through what he termed "hundreds of thousands of pages" of documents.

Although a provisional date had been set for late March, Judge Orie then said the Hague-based court had yet to make a final decision on a trial date.

"It still has to be considered," he said, adding Lukic's request would be included in the trial chamber's final ruling.

Speaking towards the end of the hearing, Mladic told the judge, whom he addressed as "Comrade Orie", that he objected to being handcuffed on his way to court.

Mladic again said he was a "sick man" since suffering a stroke in 2008 and complained about not being allowed to wear a hat in the courtroom to protect his head against the air conditioning.

"I am a very sick man, and perhaps it's God's will," Mladic said, adding "I carry a heavy burden and I have been for a while."

Arrested in Serbia on May 26 after 16 years on the run, the man also dubbed the Butcher of Bosnia has denied the charges.

This included responsibility for the July 1995 Srebrenica massacre when more than 7,000 Muslim men and boys were killed over a period of six days. It was Europe's worst war-time atrocity since World War II.