The United States Securities and Exchange Commission has sued Elon Musk, arguing that his purchase of Twitter shares in 2022 was carried out with violations, the regulator said in a filing published Tuesday.

"Defendant Elon Musk failed to timely file with the SEC a beneficial ownership report disclosing his acquisition of more than five percent of the outstanding shares of Twitter's common stock in March 2022, in violation of the federal securities laws," the agency said in a court filing.

According to the SEC, the omission enabled Musk, the world's richest man and a close ally of President-elect Donald Trump, to continue purchasing shares at "artificially low prices, allowing him to underpay by at least $150 million for shares he purchased after his beneficial ownership report was due."

Alex Spiro, an attorney for Musk, called the filing a "sham" that culminated a "multi-year campaign of harassment" against the billionaire.

"Today's action is an admission by the SEC that...they cannot bring an actual case," he said in an email to AFP.

Musk's role at the social network has been marked by numerous controversies and led to various legal actions on the part of investors, former employees and companies that had contracts with Twitter, now called X.

Shareholders, for example, have filed a lawsuit against Musk, accusing him of disclosing his five percent stake in Twitter too late, after the deadline set by the SEC.