Elon Musk visited the location where a group of Thai boys and their soccer coach were trapped in a cave, according to a post on his Twitter account.

The Tesla CEO tweeted late Monday that he had “just returned from Cave 3,” likely in reference to chamber three, the rescue command center.

A “kid-size submarine” that he shared footage of on social media is “ready if needed,” the billionaire entrepreneur said, and is named “Wild Boar” after the boys’ soccer team. The 12 boys and their coach were discovered trapped inside the flooded Tham Luang cave in Thailand’s Chiang Rai province last week.

The structure of the mini-submarine was made from a part of one of space exploration firm SpaceX’s Falcon rockets.

“Leaving (it) here in case it may be useful in the future,” Musk said Monday, adding: “Thailand is so beautiful.”

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However, the proposal to rescue the children by sending them out of the cave in the vessel was reportedly not welcomed by the head of the rescue team.

According to the BBC, Narongsak Osottanakorn said that the equipment brought by Musk’s team was “technologically sophisticated” but “not practical with our mission.”

CNBC understands that Musk visited the tunnel overnight to assess the conditions in the cave and receive feedback on the mini-submarine. The team is not planning on using the submarine as it is a backup option.

Musk later refuted the BBC story, claiming that Dick Stanton, co-leader of the diving team, was the expert on the matter. In a tweet, he attached what appeared to be email correspondence with Stanton.

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Musk from SpaceX and tunneling firm The Boring Company to the cave over the weekend to examine the situation. He mulled the possibility of pumping water through it to retrieve the boys and their coach, and also suggested inserting a nylon tube into the cave to inflate it with air “like a bouncy castle.”

Thai Prime Minister General Prayut Chan-o-cha said the tools Musk brought to Thailand were "useful" and could possibly be "modified and adjusted for future use," according to a transcript of a press briefing he gave on Tuesday.

“Multiple divers involved with the rescue said the mini-sub design was viable, and their feedback directly informed our engineering and testing,” a spokesperson for The Boring Company said in an emailed statement.

On Tuesday afternoon local time, it was confirmed by the Thai Navy Seals that all of the boys and their coach were rescued from the cave.