"We request Mr Karadzic to attend so that his trial is not further obstructed," O-Gon said.
Karadzic opted to defend himself in the trial, although he has no legal background, saying he needs more time to prepare his defence.
He faces 11 counts of genocide and war crimes for allegedly masterminding Serb atrocities during the 1992-95 Bosnian war.
The bloodiest conflict seen in Europe since the second world war left an estimated 100,000 people dead.
Among the key charges Karadzic faces is one count of genocide over the massacre of Muslim men and boys at the UN-protected enclave of Srebrenica in July 1995, in which about 8,000 people died.
He also faces another genocide charge over the siege of Sarajevo.
Barnaby Phillips, Al Jazeera's correspondent in the Bosnian capital, said: "People here are a little bit disappointed. Sarajevo had a terrible time during the war, it was actually under siege for 44 months.
"From early 1992 to towards the end of 1995 more than 10,000 people were killed here and yet this trial has got off to a very messy, a very inconclusive start."
Issue of lawyer
Tim Friend, Al Jazeera's correspondent at The Hague, said: "We're seeing a hint of how he is going to play this.
"When you represent yourself, you have more chance of delaying a trial than when you have a lawyer appointed - the latter conform to the strictures of the court and progress is made.
"I think he probably learned something from his previous trial. If he continues not to appear, it is my understanding he will have a lawyer imposed upon him."
Axel Hagedorn, a lawyer for the mothers of Srebrenica, told Al Jazeera that the court has a tough decision to make regarding whether they give him a lawyer or more time.
"In both cases it will delay the case, " Hagedorn said.
"If a new lawyer comes in he will have to prepare himself, I would say for at laest one year ... and if they don't do it Karadzic might get three more months, and in the long term he might do it again."
Serge Brammertz, chief prosecutor in the case, said: "We hope to be able to prove the criminal intent and to show that it was a planned operation - ethnic cleansing, genocide - planned in advance, implemented by Karadzic, Mladic and a number of other persons," Brammertz said.
Al Jazeera's Tim Friend reports on Karadzic's decision to boycott the opening of his trial
"This trial is important for the victims who will finally see justice being done," he told the AFP news agency.
Karadzic has repeatedly refused to enter pleas, but insists he is innocent.
According to the charge sheet, he 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."
His trial is expected to last for up to two years and he faces a maximum sentence of life in jail if convicted.
Karadzic was arrested in Belgrade last July after 13 years on the run.
He had been posing as New Age healer, named Dr Dragan Dabic, and had disguised behind thick glasses a bushy beard and straggly gray hair.
Prosecutors had wanted to try Karadzic alongside his wartime military chief, General Ratko Mladic, but Mladic has yet to be apprehended - one of two suspects still sought by the court.
The other is Goran Hadzic, a former leader of rebel Serbs in Croatia.