Florence Hartmann, the former spokeswoman for the chief prosecutor at the UN court in The Hague, says that successive Russian and American administrations, with British and French connivance, have obstructed all efforts to arrest and try Karadzic, the former president of the breakaway Bosnian-Serb republic. On one occasion in 1997, Hartmann says, a Russian aircraft flew Karadzic to Belarus where he hid for several months. On another occasion in May 1997, then US president Bill Clinton and Tony Blair persuaded the former French president Jacques Chirac that Russia should be informed before Karadzic could be arrested. Chirac protested that the then Russian president, Boris Yeltsin, would immediately tip off the wanted man. The French president was persuaded to give way.

More recently, in 2004, she says, American forces tipped off Karadzic that he was to be arrested by the new democratic government in Serbia. Karadzic has been indicted on two counts of genocide for the mass slaughter of Bosnian Muslims and Croats. He is on the run and believed to be in Bosnia or Montenegro.

In her book, Paix et Chatiment (Peace and Punishment), to be published next week, Hartmann, a former French journalist, draws on her experiences as chief spokesperson until last year for Carla Del Ponte, the Swiss-born chief prosecutor at The Hague. She says Del Ponte was told by Chirac that the US blocked the arrest of Karadzic as part of a secret agreement made at the Balkan peace talks in 1995. She also speculates that western governments may have preferred to see Karadzic free rather than risk revelations about the passivity of UN forces during the massacres of Bosnian Muslims.

In extracts from her book, Hartmann recalls a meeting between Clinton, Blair, Chirac and the former German chancellor Helmut Kohl at the Elysee Palace in Paris in May 1997. Chirac still wanted revenge for the capture of two French pilots shot down and held hostage by Bosnian Serb forces in 1995. He wanted the west to act immediately on information about Karadzic's latest hiding place. "Bill Clinton stressed that the operation could not be undertaken without informing the Russians. Chirac was opposed because Moscow had firmly opposed the arrest of Karadzic and would have immediately tipped him off, " Hartmann said. "Clinton insisted, supported by Blair. Chirac ended up by conceding the issue."

Later, she says, Chirac told Del Ponte that Karadzic could not be arrested because of Russian opposition. She quotes Chirac as telling the prosecutor, "Boris Yeltsin told me: 'Karadzic knows too much about [Slobodan] Milosevic [who was Yugoslav president at the time].'

"He warned me he would send a plane to get him out of Bosnia if necessary, but he would never permit the arrest of Karadzic."