Elon Musk has escalated his baseless attacks against a British diver by claiming without evidence the man who helped rescue children from a cave in Thailand was a “child rapist” in an email to a reporter.

The embattled Tesla CEO faced widespread backlash in July when he first called the diver Vernon Unsworth a “pedo” in a tweet - an unfounded claim against a man who was part of the international team that freed 12 young footballers and their coach from the Tham Luang cave complex.

Mr Musk, who had unsuccessfully attempted to assist the rescue mission, eventually apologised to Mr Unsworth.

On Tuesday, however, BuzzFeed published two new emails from Mr Musk, in which he called a journalist who has written about the dispute a “fucking asshole”, and he made new extraordinary claims against Mr Unsworth, without providing documentation to support the allegations.

Mr Musk called Mr Unsworth a “single white guy from England who’s been traveling to or living in Thailand for 30 to 40 years”, alleging he had moved to Chiang Rai “for a child bride who was about 12 years old at the time”. He asserted that the city was “renowned for child sex-trafficking”.

BuzzFeed reported it had investigated the allegations and Mr Unsworth’s background but could not verify any of the claims and said that it was unclear where the allegations originated.

Mr Unsworth, who said he was considering legal action after the original insults on Twitter, is now moving forward with a lawsuit, his lawyer said in an email to the Guardian on Tuesday: “Elon Musk’s campaign of publishing vile and false accusations against Mr Unsworth is inexcusable. Musk hopes to be sued and he deserves to be sued. He will be.”

Mr Musk’s email to BuzzFeed, which was a response to Mr Unsworth’s latest legal threats, said: “I suggest that you call people you know in Thailand, find out what’s actually going on and stop defending child rapists, you fucking asshole ? As for this alleged threat of a lawsuit, which magically appeared when I raised the issue (nothing was sent or raised beforehand), I fucking hope he sues me.”

Mr Musk also defended his original effort to help the rescue mission in a follow-up email.

The Tesla CEO confirmed to the Guardian on Tuesday that he had sent the email but did not immediately comment further. Tesla did not respond to a request for comment.

BuzzFeed said it could not locate any UK criminal records for Mr Unsworth (63) and also spoke with his girlfriend, who said she was 40 and had been with him for seven years.

The controversy comes at a time when Tesla and Mr Musk continue to battle intense negative publicity and embarrassing controversies. His seemingly impulsive tweets have repeatedly led him into trouble.

Notably, Mr Musk recently tweeted that he had “secured” funding to take his electric car company private, which prompted scrutiny from the Securities and Exchange Commission and backlash from investors.

Earlier this year, Tesla’s credit rating was downgraded to negative, with Moody’s citing a “significant shortfall” in the Model 3 production rate. The CEO also faced criticism after he criticised analysts on an earnings call in the spring, saying they should stop asking “boring, bonehead questions”.

After the first attack on Mr Unsworth, some investors demanded an apology and criticised Mr Musk for distracting from Tesla’s mission. – Guardian