PARIS, France (AFP) — American international grandmaster Hans Niemann said he "won't back down," after the chess platform chess.com reported that he has "probably cheated more than 100 times" in online games.

Norwegian world champion Magnus Carlsen last week accused 19-year-old Niemann of cheating.

"Overall, we have found that Hans (Niemann) has likely cheated in more than 100 online chess games, including several prize money events," the world's leading online chess platform wrote in a Tuesday evening report that ran 20 pages, with 50 additional appendices.

Chess.com banned Niemann on 5 September, shortly after the first accusations were made, but the platform is defending itself against suggestions that it is under pressure from Carlsen, whose Play Magnus company it is in the process of buying.

After a victory in the US Chess Championship Wednesday, Niemann said the game he had just won "spoke for itself and showed the chess player that I am."

He added that "it also showed that I'm not going to back down and I'm going to play my best chess here regardless of the pressure that I'm under but declined to comment further."

Chess.com said it is "extremely confident" in its means of detecting cheating, which includes using grandmasters — the highest rank of chess players — as well as an analysis of moves made by computer programs.

The suspicions of the platform go beyond the framework of the Internet. It also devotes part of its report to Niemann's spectacular and rapid progress on the chessboard.

"While we do not doubt that Hans is a talented player, we note that his results are statistically extraordinary," said the report that illustrated the American's rise with a dramatic graph.

Chess.com, however, said it had no evidence that Niemann had cheated in "over-the-board" games when players are physically present.