This is the first time Billionaire Elon Musk has threatened to walk away from the deal in writing as opposed to airing it on Twitter's social media platform.

Musk has told both securities regulators and Twitter that the social media company has committed "a clear material breach" of its "obligations under the merger agreement and Mr. Musk reserves ... his right not to consummate the transaction."

The filing marks an escalation of Musk's prior statements that have highlighted fake accounts as a threat to his proposed $44 billion deal to take over Twitter.

Musk has said that the real number of "'bots" [automated computers running tasks] may be four times higher than Twitter estimates.

Bots can be used on social media to spread false news or create a distorted impression of how widely information is being consumed and shared.

Twitter chief executive Parag Agrawal has said that fewer than five percent of accounts active on any given day at Twitter are bots, but that analysis cannot be replicated externally due to the need to keep user data private.

In March, Musk said he would put the deal "temporarily on hold", while he waits for the social media company to provide data on the proportion of its fake accounts.

"Musk believes Twitter is transparently refusing to comply with its obligations under the merger agreement, which is causing further suspicion that the company is withholding the requested data," according to the letter.

A self proclaimed free-speech absolutist, Musk has questioned the accuracy of Twitter's public filings about spam accounts representing less than 5% of its user base, claiming they must be at least 20%.

Musk said he needed the data to conduct his own analysis of Twitter users and did not believe in the company's "lax testing methodologies."

Twitter did not immediately respond to a request for comment.

This article was compiled from information furnished by Reuters and Agence France-Presse