THE HAGUE - Radovan Karadzic boycotted the start of his UN genocide trial on Monday and the judge accused the Bosnian-Serb wartime leader of obstructing the event.

Karadzic, the political leader during Bosnia's 1992-95 war which left at least 100,000 dead and became notorious in history because of the Srebenica massacre and siege of Sarajevo, refused to attend because he says he needs more time to prepare.

Neither Karadzic nor any of his legal advisors were present at the International Criminal Tribunal for the former Yugoslavia (ICTY) when judge O-Gon Kwon started the hearing which lasted less than 15 minutes.

Noting the absence, Kwon adjourned the hearing until Tuesday and issued an appeal, to "again encourage Mr Karadzic to attend the proceedings."

But he also launched an early warning at Karadzic, who was detained in Belgrade in July 2008 after 13 years on the run.

Kwon said the court could impose a defence lawyer on Karadzic, among other measures, should he display "consistently obstructive behaviour".

"We request Mr Karadzic to attend so that his trial is not further obstructed," he said.

Kwon and the other judges now have to decide whether to proceed in his absence, have him brought to the court by force, impose a defence lawyer on him or give in to his demand for more time.

Karadzic, 64, faces 11 charges of genocide, war crimes and crimes against humanity for his role in the war. He denies all charges but risks a life jail sentence if found guilty.

The new hearing on Tuesday afternoon should be devoted to hearing the charges put by prosecutor Alan Tieger.

Karadzic stands accused of having "participated in an overarching joint criminal enterprise to permanently remove Bosnian Muslim and Bosnian Croat inhabitants from the territories of Bosnia Hercegovina claimed as Bosnian Serb territory," according to the charge sheet.

Key among the charges is the massacre of more than 7,000 Muslim men and boys at the UN-protected enclave of Srebrenica in July 1995, as well as the 44-month siege of Sarajevo that ended in November 1995. The victims are still being dug out of mass graves in Bosnia.

The indictment also lists the killings of hundreds of civilians on Bosnian roads, in their homes and in detention camps in more than a dozen other municipalities.

The former president of the self-proclaimed Serb Republic in Bosnia, Karadzic is accused of having committed these crimes in his pursuit of a "Greater Serbia" which was to include 60 percent of the territory of Bosnia.

He is alleged to have worked with Yugoslav strongman Slobodan Milosevic, who died midway through his own UN genocide trial in March 2006.

In a document filed with the court, Karadzic has insisted he "never planned, instigated, ordered, committed or otherwise aided and abetted any of the crimes charged."

The "great powers" orchestrated the war in Bosnia, he claimed in a written interview with AFP "to achieve imperial goals."

In a bid to avoid the dock, Karadzic has repeatedly claimed that he reached an agreement with US diplomat Richard Holbrooke in 1996 which guaranteed him immunity from prosecution in return for his withdrawal from public life.

The court has repeatedly rejected the claims, saying that even if such a deal existed it could not stop the trial.

Karadzic's former right-hand man, Bosnian Serb general Ratko Mladic, is still on the run.