Elon Musk has threatened to sue US media watchdog Media Matters and those who attacked his social media platform X, following moves by several large American companies to halt advertising on the site after being promoted alongside antisemitic content.

“The split second court opens on Monday, X Corp will be filing a thermonuclear lawsuit against Media Matters and all those who colluded in this fraudulent attack on our company,” Musk wrote in a post on X, without naming any other parties, a Reuters report said on Saturday.

Musk and X have been under a microscope all of last week for antisemitic and racist content that has proliferated on the site since he purchased it in 2022.

Liberal watchdog group Media Matters for America said last week that it found ads from IBM, Apple and others were placed alongside content promoting Adolf Hitler and the Nazi Party.

Musk on Wednesday endorsed an antisemitic post on X that falsely claimed members of the Jewish community were stoking hatred against white people, drawing sharp condemnation, including from the White House.

Numerous companies suspended ads in the last two days, including IBM, Disney, Warner Bros Discovery and Comcast, Lions Gate Entertainment and Paramount Global. Axios reported that Apple, the world’s largest company by market value, would do the same.

“This week Media Matters for America posted a story that completely misrepresented the real experience on X, in another attempt to undermine freedom of speech and mislead advertisers,” a statement posted by Musk said. He accused Media Matters of creating an alternative account designed to “misinform advertisers” about their posts.

Media Matters on Saturday said Musk was a “bully” who threatens “meritless lawsuits”.

“Musk admitted the ads at issue ran alongside the pro-Nazi content we identified,” Media Matters President Angelo Carusone said in a statement, adding, “If he does sue us, we will win.”

Musk has threatened legal action against other parties in the past, most specifically the Anti-Defamation League, a non-profit organization that fights antisemitism, blaming it for X’s loss of ad revenue. He has not yet sued the ADL, however.

Advertisers have fled the site since Musk bought it in October 2022 and reduced content moderation, resulting in a sharp rise in hate speech, according to civil rights group.