The Norwegian suggested that his opponent's rise is "unusual" and admitted he became suspicious that the American was cheating during their Sinquefield Cup match earlier this month due to his mannerisms.

Carlsen, who has not clearly commented on the controversy publicly until now, revealed this was the reason behind him unexpectedly withdrawing from the competition after he lost.

"When Niemann was invited last minute to the 2022 Sinquefield Cup, I strongly considered withdrawing prior to the event," his statement read.

"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 only think a handful of players can do.

"This game contributed to changing my perspective."

Niemann remarked after his stunning victory that he felt "bad" for Carlsen because "it must be embarrassing for the world to lose to me".

The American, 19, has admitted to cheating in online competitions when he was younger but has rejected any allegations he used foul play to upset Carlsen.

He is insistent that he is "clean" and is willing to play naked to prove his innocence.

Niemann has claimed those who are levying the allegations against him are attempting to ruin his career.

Sinquefield Cup chief arbiter Chris Bird said "no indication" of cheating by any player was found at the event.

Following his in-person defeat, Carlsen then pulled out of his online Meltwater Champions Chess Tour's Julius Baer Generation Cup game versus Niemann after just one move, causing the sport to be rocked again.

Chess.com, an online website where chess players can compete, has alleged it believes Niemann has cheated more than he has revealed and has even shown him evidence to support their claim.

The platform has banned Niemann from their site and events.

Carlsen called cheating in chess "a big deal and an existential threat to the game" and proposed for competition organisers to "seriously consider increasing security measures and method of cheat detection for over the board chess".

The five-time world champion has affirmed that he will not playing against opponent he believes to have cheated, including Niemann.

He said: "We must do something about cheating, 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."