Elon Musk has reignited his attack on a British cave diver who helped rescue a Thai boys soccer team by making the unsubstantiated accusation that he moved to the Asian country to take a child bride.

The Tesla CEO has previously accused Vernon Unsworth of being a "paedo guy" after he helped free the 12 boys trapped in a flooded Thai cave in July.

Musk later apologised and deleted a series of tweets that alleged the 63-year-old was a paedophile, but he revived the claim again last week in yet another Twitter tirade in which he questioned why the diver hadn't brought legal action.

Now the billionaire has made further allegations against Unsworth in a series of rambling emails he sent to Buzzfeed News that were published on Tuesday.

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"I suggest that you call people you know in Thailand, find out what's actually going on and stop defending child rapists, you f***ing a**hole," Musk's email read.

"He's an old, single white guy from England who's been traveling to or living in Thailand for 30 to 40 years, mostly Pattaya Beach, until moving to Chiang Rai for a child bride who was about 12 years old at the time."

Musk added: "I f***ing hope he sues me."

Unsworth's attorney denied the most recent allegations made by Musk.

The British diver has been dating his 40-year-old Thai girlfriend for seven years.

Musk's dispute with Unsworth began back in July when the Thai children were all safely retrieved from the cave where they had been trapped for days.

Unsworth had publicly criticized Musk's offer to build a child-sized mini submarine to help free the trapped children.

The rescue mission to save the Thai soccer team. Photo / Elon Musk Twitter
The rescue mission to save the Thai soccer team. Photo / Elon Musk Twitter

The diver, who splits his time between the UK and Thailand, had told Musk to "stick his submarine where it hurts", adding that the offer was a "PR stunt" that "had absolutely no chance of working".

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Musk then hit back in a bizarre series of tweets in which he pledged to produce videos proving the sub would have worked.

"Sorry paedo guy, you really did ask for it," he said of Unsworth.

The remarks created a furore and drew a backlash from Tesla's board of directors.

Unsworth said at the time that he would weigh his legal options when he was back in the UK.

Musk issued an apology on July 18 at the urging of the Tesla board.

"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," Musk said.

"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."

The matter seemed to have been resolved following the apology - until the Tesla CEO reversed himself and revived the claim in a Twitter tirade last week.

"You don't think it's strange he hasn't sued me? He was offered free legal services," Musk wrote, responding to a tweet from a former TechCrunch writer criticising the "paedo guy" remark.

"Did you investigate at all? I'm guessing answer is no. Why?" Musk continued. "Answer the question @yoda. You brought it up, not me. Did you investigate or not? If so, what did you actually do?"

Just last week, Unsworth's mother Vera confirmed her son was taking legal action against Musk over his comments.

"He's consulted his lawyer this morning. That's all he's told me," she said from her Essex home.

"I don't know who his lawyers are or where they're based. My son is in London on business at the moment but he's asked me not to comment any further."

Musk's increasingly erratic behavior on Twitter - including an announcement he later retracted that Tesla would be taken private, causing trading in the company's shares to be halted - led to a New York Times interview in which he confessed to be exhausted from constant work.