US chess grandmaster Hans Niemann's lawsuit against those who accuse him of cheating is baseless, a gaming group partly owned by his main accuser, world champion Magnus Carlsen, said.

Carlsen has publicly accused Niemann of cheating, and Chess.com alleged in a report earlier this month that the 19-year-old American has "probably cheated more than 100 times" in online games.

Niemann, 19, responded by last week filing a US lawsuit seeking $100 million in damages from Carlsen, his company Play Magnus Group, Danny Rensch of Chess.com, the world's leading online chess platform, and American grandmaster Hikaru Nakamura.

Niemann accused them of slander, libel and colluding to destroy his reputation and livelihood.

"The company is surprised by this complaint and finds no merit in the claims", Play Magnus said Tuesday.

"Play Magnus is conferring with legal counsel regarding any potential actions".

31-year-old Carlsen, the five-time reigning world champion, owns 8.54% of the company, which is in the process of being sold to Chess.com.

The controversy began after Niemann beat Carlsen at the Sinquefield Cup tournament in Missouri on September 4.

Carlsen then withdrew from the tournament, accusing his opponent of cheating.

The allegations, which he has reiterated several times since then, were subsequently repeated by Nakamura and Chess.com.

Niemann has accused his critics of having acted together out of financial interests.

While he has admitted cheating on Chess.com when he was 12 and 16, he said he stopped after that and is ready to play "fully naked" to prove his talent.

His lawsuit has been filed with a US federal court in Missouri. 

Meanwhile, the international chess federation FIDE has opened an inquiry into the allegations.