World chess champion Magnus Carlsen said on Monday he believes Hans Niemann has "cheated more -- and more recently -- than he has publicly admitted" and that he no longer wants to play against the American or another player who has cheated in the past.
Carlsen, world champion since 2013, withdrew from the Sinquefield Cup in St. Louis, Missouri earlier this month after unexpectedly losing to Niemann, sparking multiple comments and allegations that Niemann had cheated.
Carlsen then sent the chess community into a frenzy when, in his rematch with Niemann at the Julius Baer Generation Cup, he resigned after just one move. Niemann trails Carlsen by almost 200 Elo points -- the rating system used to calculate the relative skill levels of players.
Niemann, who has previously been banned by chess.com, has admitted cheating online twice, when he was 12 and 16, but denied ever cheating over the board, and even said he was willing to "strip fully naked" to prove his innocence. Carlsen did not provide any evidence towards his claims against the American.
"So far I have only been able to speak with my actions, and those actions have stated clearly that I am not willing to play chess with Niemann," Carlsen said in a statement on Twitter.
My statement regarding the last few weeks. pic.twitter.com/KY34DbcjLo— Magnus Carlsen (@MagnusCarlsen) September 26, 2022
"I believe that cheating in chess is a big deal and an existential threat to the game," Carlsen said.
"I also believe that chess organizers and all those who care about the sanctity of the game we love should seriously consider increasing security measures and methods of cheat detection for over the board chess.
"When Niemann was invited last minute to the 2022 Sinquefield Cup, I strongly considered withdrawing prior to the event.
"I ultimately chose to play. I believe that Niemann has cheated more -- and more recently -- than he has publicly admitted. His over the board progress has been unusual, and throughout our game in the Sinquefield Cup I had the impression that he wasn't tense or even fully concentrating on the game in critical positions, while outplaying me as black in a way I think only a handful of players can do. This game contributed to changing my perspective."
Niemann was not immediately available to comment following Carlsen's statement.
The International Chess Federation (FIDE) said last week it shared the Norwegian's concerns about cheating in the sport.
"We must do something about cheating," Carlsen added. "And for my part going forward, I don't want to play against people that have cheated repeatedly in the past, because I don't know what they are capable of doing in the future.
"There is more that I would like to say. Unfortunately, at this time I am limited in what I can say without explicit permission from Niemann to speak openly.
"So far I have only been able to speak with my actions, and those actions have stated clearly that I am not willing to play chess with Niemann. I hope that the truth on this matter comes out, whatever it may be."