The billionaire and founder of electric car maker Tesla, who earlier this month disclosed he owns a 9.2% stake in Twitter, proposed in a regulatory filing on Thursday to buy all of the company's outstanding common stock for $54.20 per share.

"I invested in Twitter as I believe in its potential to be the platform for free speech around the globe, and I believe free speech is a societal imperative for a functioning democracy," he said in the filing. "However, since making my investment I now realize the company will neither thrive nor serve this societal imperative in its current form."

Earlier this week, Musk said he had abandoned a plan to join Twitter's board, just as his tenure was about to start. Taking the board seat would have prevented him from a possible takeover of the company.

"Since making my investment I now realize the company will neither thrive nor serve this societal imperative in its current form. Twitter needs to be transformed as a private company," Musk said in a letter to Twitter Chairman Bret Taylor.

Also on Thursday, Twitter's chief executive told employees that the company was evaluating the approach. Parag Agrawal also reportedly said at the staff meeting that the company was not being "held hostage" by the offer.

Speaking at the TED2022 conference in Vancouver, Mr Musk said: "I am not sure that I will actually be able to acquire it."He added that he had a Plan B if his bid for Twitter was rejected, but gave no further details of what that could mean.