Tesla billionaire Elon Musk is being sued by the British cave explorer he called a “pedo guy”.

Vernon Unsworth, 63, a British cave explorer who was part of the huge international team involved in the July rescue of a Thai soccer team from a flooded cave, has engaged an American lawyer to take on Mr Musk.

Atlanta defamation lawyer Lin Wood told CNN on Thursday that he was “finalising the libel complaint”.

He said he had written to Mr Musk, advising him of the pending lawsuit.

“I am in the process of preparing a civil complaint for libel against you,” he wrote. “In an attempt to avoid litigation and to see the public record is corrected, I invite you or your legal representatives to contact me.”

@elonmusk should check his mail before tweeting. pic.twitter.com/3c9QWtdp25

— Lin Wood (@LLinWood) August 29, 2018

CNN said it was unclear if Mr Musk had seen the letter. But he fired up the issue again in tweets on Tuesday, appearing to suggest it was suspicious that he had not yet been sued.

You don’t think it’s strange he hasn’t sued me? He was offered free legal services. And you call yourself @yoda …

— Elon Musk (@elonmusk) August 28, 2018

The action was sparked following Mr Musk’s Twitter tirade against Mr Unsworth after the diver, who lives in Thailand, criticised the Tesla and SpaceX boss’s mini-submarine rescue plan.

Mr Unsworth, whose knowledge of the cave was crucial in freeing the boys and their coach, had told CNN Mr Musk’s prototype submarine would have had “absolutely no chance of working”.

“He can stick his submarine where it hurts,” he said. “He had no conception of what the cave passage was like. The submarine, I believe, was about 5ft 6in [168 centimetres] long, and rigid, so it wouldn’t have gone round corners or obstacles.

“It wouldn’t have made the first 50 metres in from the dive start point. Just a PR stunt.”

Mr Musk responded with a tirade of since-deleted tweets referring to the cave expert – without any foundation – as “pedo guy”. He said he would make a video proving the mini-sub would have worked, adding: “Sorry pedo guy, you really did ask for it”.

Mr Musk then tweeted to more than 22 million followers: “Bet ya a signed dollar it’s true”.

Amid a backlash, and as Mr Unsworth said he was considering legal action, Mr Musk tweeted an apology.

“My words were spoken in anger after Mr Unsworth said several untruths & suggested I engage in a sexual act with the mini-sub, which had been built as an act of kindness & according to specifications from the dive team leader,” he wrote.

“Nonetheless, his actions against me do not justify my actions against him, and for that I apologise to Mr Unsworth and to the companies I represent as leader. The fault is mine and mine alone.

“I am truly sorry if I offended anyone.”

This week, in response to Mr Musk’s latest tweets, Mr Unsworth told Britain’s Sky News that he could not comment.

“It’s all being dealt with. That’s all I can say,” he said.

Mr Wood told CNN he expects to file the lawsuit in a Los Angeles court within days.

Mr Musk already faces at least five lawsuits and a US Securities and Exchange Commission probe following his tweets about potentially taking his electric car company Tesla private. He tweeted last week that he was no longer pursuing that plan.

-with agencies