THE HAGUE, Netherlands -- Appeals judges at the Yugoslav war crimes tribunal ruled Monday that Serbian far-right leader Vojislav Seselj has breached conditions of his provisional release and must return to the court's cellblock in The Hague.

The decision means authorities in Serbia will be ordered to detain Seselj and send him back to the United Nations tribunal where he already has spent more than a decade in custody.

Seselj on Monday reiterated that he won't surrender voluntarily and challenged Serbian authorities to try to arrest him.

"Let the police come, I'll watch my back," he said. "It won't be easy arresting me."

Seselj, who is accused of recruiting notorious paramilitary forces during the Balkan wars, was released in November for medical treatment in Serbia on condition that he did not interfere with victims or witnesses and that he would return to the tribunal if summoned. Serbian doctors say he is suffering from colon cancer that has spread to his liver.

But Seselj told a news conference after arriving back in Belgrade that he would not return voluntarily. Prosecutors say such statements breached the conditions of his release and in a majority written decision appeals judges agreed.

Serbian Prime Minister Aleksandar Vucic denounced tribunal's decision as "immoral" and said the government will decide what to do "in the next few days."

Rasim Ljajic, a Serbian government official in charge of co-operation with the UN court, said the decision to seek Seselj's return is "strange and confusing, to say the least."

"By reaching two contradictory decisions within only five months, the tribunal is making our mutual co-operation significantly difficult," Ljajic said.

Seselj surrendered to the court in 2003 and is awaiting verdicts in his trial that was repeatedly delayed.

UN prosecutors have demanded a 28-year prison sentence for Seselj. They said his hate speeches at rallies "planted the seeds of ethnic hatred and helped them grow into ethnic violence against non-Serbs."

He was charged with war crimes including planning the capture of towns in Croatia and Bosnia as part of a criminal plot involving other Serb leaders, including former strongman Slobodan Milosevic, to drive out non-Serbs using massive destruction and terror. He insists he is innocent.

Associated Press writer Dusan Stojanovic contributed from Belgrade, Serbia.