THE HAGUE, Netherlands - Radovan Karadzic has threatened to boycott his genocide trial at the Yugoslav war crimes tribunal, saying in a letter released Thursday he needs more time to prepare.

The former Bosnian Serb leader told judges at the UN court he should have been given two years to get ready for the "gigantic" case.

"The biggest, most complex, important and sensitive case ever before this tribunal is about to begin without proper preparation," he wrote.

Tribunal spokeswoman Nerma Jelacic said his trial would still start Monday "as previously scheduled," despite the boycott threat.

That sets up the prospect of the court's biggest trial since its ill-fated prosecution of former Yugoslav President Slobodan Milosevic starting without the suspect in court.

Milosevic died of a heart attack in 2006 before a verdict could be reached in his four-year trial for atrocities throughout the wars, which erupted as the former Yugoslavia crumbled in the 1990s.

Karadzic is charged with 11 counts of genocide and war crimes for masterminding Serb atrocities during the 1992-95 Bosnian war when an estimated 100,000 people were killed.

He is accused of orchestrating crimes including the 1995 massacre of 8,000 Muslim men in the UN-protected Srebrenica enclave and the deadly campaign of shelling and sniping during the siege of Sarajevo. He faces a maximum sentence of life imprisonment if convicted.

In his six-page letter, Karadzic tells judges assigned to his trial he is not ready and "therefore I shall not appear before you on that date."

It was not clear if he intended to stay away only for the prosecution's opening statement next week or planned a longer boycott.

Karadzic is defending himself. If he refuses to attend his trial judges may appoint a defence lawyer -- something Karadzic is unlikely to accept.

His letter said he would continue preparing his defence, "and as soon as I will be prepared, I will be happy to inform" court officials "a few weeks in advance."

Prosecution spokeswoman Olga Kavran declined to speculate on what might happen next.

"It is up to the judges to determine what to do," Kavran said. "The prosecution is ready for the trial."

If he persists with the boycott, Karadzic will remain in his cell at the court's detention unit in a seaside neighbourhood of The Hague.

Prosecutors are scheduled to make opening statements for the first two days of the case. It will then adjourn until Nov. 2 when Karadzic has two days to present his opening statement. The first witness is due to take the stand Nov. 4.

The 64-year-old was arrested in July last year on a Belgrade bus while disguised as a New Age healer.

He has repeatedly requested more time to prepare, accusing prosecutors of burying him under an avalanche of documents and other evidence.

However, judges say he has had enough time, and the court's appeals chamber agreed earlier this month, clearing the way for his trial to start.

Prosecutors say they will take about a year to present their case and Karadzic has been given the same amount of time to mount his defence.

Karadzic would not be the first former leader to boycott the start of his war crimes trial. In June 2007, former Liberian President Charles Taylor stayed in his cell and fired his attorneys on the opening day of his trial on charges of allegedly orchestrating atrocities in neighbouring Sierra Leone.

Taylor's trial was held up for months before resuming with Taylor present and a new lawyer leading his defence.