A British caver who helped rescue 12 boys from a Thai cave said Monday he may take legal action against Elon Musk after the entrepreneur called him a "pedo."

Tesla CEO Musk launched the extraordinary tirade against Vernon Unsworth without providing any justification or explanation, after the cave expert slammed his offer of a miniature submarine to extract the footballers from the Tham Luang cave as a "PR stunt."

The "Wild Boar" team were rescued last week by an international team of divers through a narrow network of twisting, flooded tunnels.

Unsworth, who provided mapping knowledge of the cave to rescuers, said Musk's prototype would have had "absolutely no chance of working."

"It just had absolutely no chance of working. He had no conception of what the cave passage was like. The submarine was about five foot six [inches] long, rigid, so it wouldn't have gone 'round corners or 'round any obstacles. It wouldn't have made the first fifty metrers into the cave... just a PR stunt."

Musk responded Sunday in a bizarre series of tweets referring to Unsworth, without using his name, as "pedo guy." "Pedo" is short for paedophile.

In response, Musk questioned Unsworth's involvement in the rescue, describing him as a "suss" (suspicious) "British expat guy who lives in Thailand."

Musk also said he would prove his submarine was up to the task by sending it into the cave.

"Sorry pedo guy, you really did ask for it," the 47-year-old tweeted.

When challenged by a Twitter user about the allegation leveled against Unsworth, Musk replied "Bet ya a signed dollar it's true."

The tweets have been obtained by technology news site Gizmodo.

Musk later deleted the tweets and did not immediately respond to a request for comment through Tesla.

Unsworth told AFP on Monday he had not reviewed the tweets in full and had only heard about them.

But asked if he would take legal action against Musk over the allegation, Unsworth said: "If it's what I think it is yes."

The caver said he would make a decision when he flies back to the UK this week, but added that the episode with Musk "ain't finished".

'Life and death'

Unsworth was part of an international team of cave-diving experts that rescued the group of 12 teenage boys and their coach last week. The "Wild Boars" football team had been stuck in the cave since June 23.

The rescue involved scuba diving through narrow passageways that remained totally submerged in water.

In the midst of the operation, Musk tweeted on Tuesday, apparently from Thailand: "Just returned from Cave 3. Mini-sub is ready if needed. It is made of rocket parts & named Wild Boar after kids' soccer team. Leaving here in case it may be useful in the future."

When asked about Musk being in the cave, Unsworth shrugged and said: "and [he] was asked to leave very quickly, as he should have been."

The group are currently recovering in hospital in Chiang Rai and are expected to be discharged this week.

Reports emerged Monday that two Australian divers who took part in the rescue had obtained diplomatic immunity before the operation in case it failed.

Anaesthetist Richard Harris and diver Craig Challen were protected from prosecution if anything went awry following negotiations between Australian and Thai authorities, according to Australian broadcaster ABC.

Challen said the divers had been uncertain if they would be able to save all 12 boys and their coach in the "life and death" rescue mission.

"It wasn't dangerous for us, but I can't emphasize enough how dangerous it was for the kids," he told Perth's Sunday Times.

Musk's tweets attacking Unsworth prompted condemnation from those who took part in the mission to save the boys.

Claus Rasmussen, a Danish national and instructor at Blue Label diving in Phuket, called the allegations "inappropriate" and praised Unsworth's role in the rescue.

"He was one of the driving forces in getting everything done and clarifying for us divers what was going on," he told AFP.

Musk had earlier triggered controversy after tweeting that the Thai rescue chief, who had declined the submarine prototype offer, was not really in charge of the operation.

"He's just a PR stunt merchant -- that's all he is," Unsworth said.