Elon Musk has again attacked a British diver he has previously accused without evidence of being a child abuser.
In an email to a reporter, Mr Musk said Vernon Unsworth - who assisted with the rescue of 12 Thai teenagers from a flooded cave - was a "child rapist".
Mr Unsworth's lawyer said the allegation was "completely false".
Mr Musk had earlier apologised for calling Mr Unsworth a "pedo". The pair first clashed over Mr Musk's offer of a mini-submarine to help with the rescue.
The Briton had told CNN that the submarine was "just a PR stunt [that] had absolutely no chance of working". The Tesla founder responded with a series of tweets accusing Mr Unsworth of paedophilia without providing any evidence.
In July he deleted the tweets but last week he appeared to repeat his allegation, tweeting that it was "strange he hasn't sued me" after Mr Unsworth said he was considering legal action.
What did Musk say?
Writing in an email to Buzzfeed reporter Ryan Mac, Mr Musk went further. He told the reporter to "call people you know in Thailand, find out what's actually going on and stop defending child rapists".
He alleged that Mr Unsworth, 63, had spent decades visiting and living in Thailand and had recently moved to Chiang Rai in northern Thailand "for a child bride who was about 12 years old at the time".
"It isn't where you'd go for caves, but it is where you'd go for something else," Mr Musk wrote. "Chiang Rai is renowned for child sex trafficking." He added that he hoped Mr Unsworth would sue him.
What is Unsworth's response?
Mr Unsworth's lawyer Mark Stephens from the firm Howard Kennedy told the BBC that Mr Musk's allegations were baseless.
"Just as we get a series of legal proceedings drafted, Mr Musk adds another libel to it," he said.
"He seems to have a reckless indifference about the truth of these things. There's not a shred or scintilla of evidence to back it up.
"Vernon Unsworth is in most people's minds a hero. He is not a paedophile as is alleged. We feel very strongly that the record should be put straight."
"This is all about being upset that - as one of the divers, not my client, put it - Musk's shiny tube wasn't used," he added.
Mr Stephens confirmed that Mr Unsworth was in a relationship with Woranan Ratrawiphukkun, a Thai woman who told Buzzfeed she was 40 and had been in a relationship with Mr Unsworth for seven years.
The couple had met in London, where Mr Unsworth lives, and the relationship had continued while Mr Unsworth was in Thailand exploring the Tham Luang cave complex, Mr Stephens said.
What other allegations does Musk make?
In his email, Mr Musk also said that Mr Unsworth had not been part of the cave dive rescue team and had been shunned by its members.
Mr Unsworth did not take part in the dives but had previously explored the cave complex extensively.
He knew about the raised ledge known as Pattaya Beach where the boys and their football coach could have sought shelter, travelled into the caves shortly after they went missing and called in the two expert British divers who eventually found the trapped group.
Several divers told Buzzfeed that he had worked continuously on the rescue. "He was pivotal to the entire operation," said British diver Rick Stanton.
Mr Musk also sent a copy of a letter from the Thai government thanking him for his offer of assistance and denied that he had been asked by the Thai government to leave the cave complex during the rescue operation - an assertion he alleged Mr Unsworth had made during his CNN interview.
In the interview, Mr Unsworth said Mr Musk had been asked to leave the cave complex during the rescue operation but did not say by whom.
Mr Stephens said Mr Musk had not initially asked for or been given surveys of the cave system when offering the use of a mini-submarine and it would not have fitted through the spaces available in the cave anyway. Mr Musk only arrived at the cave complex when eight of the boys had already been rescued, Mr Stephens said.
Does Musk 'attract drama'?
The latest controversy follows weeks of erratic behaviour on social media.
In July he shocked investors by announcing on Twitter that he had funding secured to take his car firm Tesla private. He later said the firm would stay public.
He also tweeted that he suffered from "great highs, terrible lows and unrelenting stress". He also tweeted that he might suffer from bipolar disorder but then said "maybe not medically".
In August he told the New York Times that he worked "120-hour weeks" and took sedatives.
His brother Kimbal Musk told the newspaper that the reason Mr Musk "seems to attract drama" is because he is "so transparent, so open, in a way that can come back to bite him".