Radovan Karadzic insisted in a letter published Friday that he was promised immunity from prosecution by the United States in 1996 - a claim strongly denied by Richard Holbrooke and Carl Bildt, both involved in diplomacy to end the 1992-95 Bosnia war.

The four-page letter was published by the International Criminal Tribunal for the former Yugoslavia (ICTY) before which the former Bosnian-Serb leader and war crimes suspect went on trial Thursday on 11 charges including genocide and crimes against humanity.

In the letter, Karadzic, 63, writes that former US mediator Richard Holbrooke promised his political representatives that Karadzic would not have to appear before the ICTY provided he withdrew from the public arena.

"Mr Holbrooke obligated himself on behalf of the US that I would not be tried before this tribunal," according to a translation of the letter released by the court.

Karadzic also referred to remarks he made during his initial appearance about fearing he would be killed while in the UN detention centre in Scheveningen, near The Hague.

"It is clear that, due the fact that the agreements he (Holbrooke) made on behalf of the US were not implemented, he has moved on to plan B - the liquidation of Radovan Karadzic."

Holbrooke, in a number of media interviews Thursday, vehemently denied having made any deal with Karadzic, calling the claim an "outrageous fabrication by a war criminal" and saying a deal would have been "unethical and immoral."

Holbrooke told Dutch television that owing to continued refusal by NATO in 1995 and 1996 to arrest Karadzic, he had been forced to negotiate with Karadzic's representatives about an agreement with the Bosnian-Serb leader to pull back from the public arena.

"This agreement was signed on July 18, 1996. But I did not give Karadzic anything in exchange," Holbrooke emphasized, "and it would have been a lot better had someone ordered NATO to arrest him when it was still possible."

Rumours about a possible deal between the US and Karadzic are not new. In her recently published book, Florence Hartmann, a former assistant to former ICTY prosecutor Carla Del Ponte, claimed the same, as has former Bosnian ambassador Mohammed Sacirby.

Holbrooke laughed about Karadzic's expressed fears that the US envoy's "long arm" might endanger his life in the UN detention centre.

"In a way it is flattering that he thinks my arm reaches to The Hague," Holbrooke said. "But the truth is, I am just an ordinary citizen and Karadzic is where he should have been a long time ago - at the ICTY."

Karadzic's claim of a deal was also denied Friday by Swedish Foreign Minister Carl Bildt, who served as an international envoy in the Balkans in the 1990s.

"There was never any such deal," Bildt told Swedish radio news. "There were no efforts to drop the charges (against Karadzic)," Bildt added, saying that he and Holbrooke were "active" in efforts to get Karadzic arrested.

Karadzic also claimed in his letter that he had become the object of a "media witchhunt," meaning he would never receive a fair trial at a UN war crimes tribunal. His branding as a war criminal by the press made an acquittal "unimaginable."