The war crimes trial of Serbian nationalist Vojislav Seselj resumed on Tuesday after a year's delay, with witnesses testifying behind closed doors to protect their identity, an issue that has dogged the trial.

Seselj faces life in prison if convicted of inciting violence against Bosnians and Croatians in the former Yugoslavia during the 1990s while head of the Serbian Radical Party.

He has pleaded not guilty to 15 counts for crimes committed between 1991 and 1993, including torture, murder and forced deportation of non-Serbs by his party's militia.

The trial, which began in late 2007 at the International Criminal Tribunal for the former Yugoslavia (ICTY) in The Hague, was halted nearly a year ago after prosecutors said the case had been compromised by threats against a witness.

In the latest twist in the case, six witnesses said they now wanted to testify on behalf of the defence -- instead of the prosecution. They will now be called by the judges hearing the case, rather than by the defence or the prosecution.

The trial is expected end this year after judges call the six witnesses, with the judges to hand down their verdict after several months' deliberation.

Seselj was sentenced to 15 months in prison in July 2009 by the tribunal for contempt of court after he disclosed the identity of three protected witnesses in a book he admitted authoring. He will start serving his term after the current trial ends.

Ahead of Tuesday's witness testimony, Seselj made several requests of the court, including permission to address the Serbian public this month ahead of a regional election there.

"Over these seven years I have had a great many problems in my profession, in my active pursuit of political life," Seselj, who surrendered to the court in 2003, told the judges.

"I'm very very interested in the outcome of these elections... I would like to address the public and present my political views that are important for me and my political party, the Serb Radical Party," he said.