According to the sources, differences between the 48-year-old Karpov and the International Chess Federation (Fide) could not be overcome.

Karpov charged that he had not been consulted by Fide's Russian president, Kirzan Ilyumzhinov, about the scheduling of the event and that he had previous commitments in August which he could not cancel.

Two weeks ago, during a tournament in Dortmund, Germany, Karpov had indicated that he was willing to take part if Fide would indemnify him for losses. However, the chess federation turned him down.

Karpov's Swiss lawyer, Alban Brodbeck, said in Lausanne that no problem would have arisen had the Fide coordinated the schedule with Karpov.