THE HAGUE, Netherlands - Former Bosnian Serb leader Radovan Karadzic has refused to answer key questions about Serb atrocities during the Bosnian war in his first appearance as a witness at the Yugoslav war crimes tribunal.

Karadzic testified at an appeals hearing for his friend and political ally Momcilo Krajisnik.

Krajisnik is appealing his 2006 conviction for helping orchestrate the murder or displacement of thousands of non-Serbs during the war.

The hearing had been seen as a preview of how Karadzic will conduct his defence when his own war-crimes trial starts, likely next year.

It was also seen as a chance for prosecutors to elicit incriminating evidence from Karadzic, who was arrested in July after 13 years on the run.

Karadzic faces charges that include genocide and crimes against humanity for allegedly masterminding atrocities by Bosnian Serb forces throughout the war that left tens of thousands dead.

The tribunal entered not guilty pleas on his behalf after Karadzic refused to enter pleas.

Karadzic's American lawyer, Peter Robinson, prevented Karadzic answering some prosecution questions Wednesday, calling them "nothing more than a transparent attempt to use his answers against him at his own trial."

When Karadzic did give answers he went into a level of detail that prosecutor Alan Tieger suggested was intended to waste time. Tieger had only 90 minutes to question Karadzic.

"That is not an answer, that is a filibuster," a frustrated Tieger told Karadzic after one rambling response.

Karadzic's political mentor, former Yugoslav President Slobodan Milosevic, used lengthy monologues to spin out his own genocide trial for more than four years. Milosevic's trial was aborted without a verdict after he died of a heart attack in his UN cell in March 2006.

Like Milosevic, Karadzic intends to defend himself at trial, but for Wednesday's hearing he used a lawyer.

Tieger set the tone with his first question, when he asked Karadzic if he denied that Bosnian Serb forces were responsible for a campaign of ethnic cleansing that included "murder and extermination of Bosnian Muslims and Croats."

Robinson immediately asked judges to allow Karadzic not to answer, saying the issue would be addressed at Karadzic's trial.

"This is neither the time nor the place," said Robinson.