San Francisco: Another day, another Elon Musk Twitter kerfuffle.

The Tesla CEO has again made implications about a rescue diver who once criticised him.

Elon Musk returned to the controversial - and some would say, counterproductive - topic on Tuesday night, launching a new round of tweets implying that the cave rescuer he accused of being a paedophile might actually be one.

On Wednesday, a lawyer said he had sent Musk a letter threatening legal action and that he's in the process of filing a libel suit against Musk on behalf of Vernon Unsworth, a diver instrumental in rescuing Thai children trapped in a cave in July.

"You published three different tweets to your twenty-two million followers that Mr Unsworth engages in the sexual exploitation of Thai children, and you did so at a time when he was working to save the lives of twelve Thai children," Unsworth attorney L. Lin Wood of Atlanta wrote in the letter.