Elon Musk has offered to buy Twitter outright in a deal that values the company at $43 billion, a filing with the US Securities and Exchange Commission (SEC) showed Thursday.

"Twitter has extraordinary potential. I will unlock it," Musk said in a letter to Twitter chairman Bret Taylor, dated Wednesday, according to the filing. Musk said his $54.20-per-share offer was his "best and final."

Twitter's stock jumped 12% pre-market.

Twitter said Thursday it had received "an unsolicited, non-binding proposal from Elon Musk to acquire all of the company's outstanding common stock" and would "carefully review the proposal to determine the course of action that it believes is in the best interest of the company and all Twitter stockholders." See more here.