The match was intended to unify the chess world

Two world champions, Russian Vladimir Kramnik and Bulgarian Veselin Topalov, are playing a series of matches. Mr Kramnik is leading after four games.

But Mr Topalov has raised questions about the amount of time his opponent is spending in the toilet.

Mr Topalov was outraged by Mr Kramnik's "suspicious behaviour", his aide said.

His manager, Silvio Danilov, had asked to see videotapes of Mr Kramnik in his designated relaxation area, in which the toilet is the only unmonitored area.

"During every game, he visited the relaxation room 25 times at the average and the bathroom more than 50 times," he said.

Mr Kramnik "takes his most significant decisions in a toilet", he said, apparently suggesting that the player was somehow cheating.

'Reality show'

Match officials have now decided that both players must use the same toilet - one in a different location - but this has not pleased either camp.

Mr Kramnik did not show up for the fifth match on Friday and said in a statement to officials that he "did not sign the contract for acting in a reality show".

"My dignity does not allow me to stand this situation," the Associated Press news agency quoted him as saying.

Mr Topalov's side, meanwhile, said the move changed nothing because Mr Kramnik would still be able to visit the toilet unlimited times.

The match had been intended to reunify the chess world, divided since then world champion Gary Kasparov split from the World Chess Federation in 1993.

Whatever the outcome, the two players were due to share the $1m (£534,000) prize.