The 53-year-old politician, who heads the Serbian Radical Party (SRS), went on trial on Wednesday at the International War Crimes Tribunal in The Hague.
He said the tribunal was created by the United Nations Security Council under pressure from the United States, not to mete out justice, but to create a world order suitable to the Americans.
"I am being tried by an illegal and illegitimate court. I am speaking of an institution that was unlawfully established... the Security Council did this on orders from the United States of America," Seselj said.
"The advocates of this world order distort the truth, and the charges leveled against me are false," he said.
Seselj surrendered voluntarily to the tribunal in February 2003. He is accused of spreading racial hatred and cooperating with former Yugoslav president Slobodan Milosevic to organize Serb paramilitaries into ethnic cleansing combat units in Bosnia, Croatia and Serbia's northern province of Vojvodina.
Hundreds of non-Serbs were subsequently killed by Serb forces Seselj recruited or influenced with his "extreme ethnic rhetoric," prosecutors say.
He said that accusations relating to the alleged genocide of 7,000 and 8,000 Muslims in 1995 were grossly exaggerated, and that the actual figure was closer to 1,000, which cannot be considered genocide.
Despite the allegations against its leader, the Serbian Radical Party remains the biggest party in the country's parliament. Seselj faces life imprisonment if convicted.
Seselj's trial began a year ago. The nationalist leader has accused the European Union, Germany, NATO, the United States and the Vatican of conspiracy against the Serbs, and promised to bring proof of this to light at his trial.
The trial, expected to last around a year, is being held place in the same courtroom where the late Slobodan Milosevic was tried. Milosevic died in detention in The Hague in March 2006 before the end of his war crimes trial.
