Biden was asked at a news conference on Wednesday whether he thought Musk was a threat to national security and if his acquisition of Twitter, with help from a Saudi Arabian conglomerate, should be investigated by the US government.

"I think that Elon Musk’s cooperation and/or technical relationships with other countries are worthy of being looked at," Biden said. "Whether he is doing anything inappropriate, I’m not suggesting that. I’m suggesting they’re worth being looked at."

Saudi Prince Alwaleed bin Talal, among the richest investors in the Middle East, and his investment firm has emerged as the second-largest investor in Twitter after Musk’s takeover of the social media platform.

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Two US senators, Democrat Ron Wyden, who chairs the finance committee, and Chris Murphy of Connecticut, last week called for a "thorough vetting" of the Twitter deal.

In a statement, Wyden said: "Given the Saudi regime’s history of jailing critics, planting a spy at Twitter, and brutally murdering a Washington Post journalist, the Saudi regime must be blocked from accessing Twitter account information, direct messages and other data that could be used to identify political opponents or suppress criticism of the royal family.

"I’ve long argued that the United States has a national security interest in protecting Americans’ data from murderous foreign governments, and this Saudi regime absolutely fits that description."

The White House said last month that reports that the US was discussing launching a national security review of some of Musk’s ventures, including Twitter, were "not true".

Musk’s purchase of Twitter has sparked concerns that he could face pressure from countries trying to control freedom of speech online.

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The world’s richest man, Musk, is CEO of electric carmaker Tesla which counts China as a key market and production base. Tesla operates a factory in Shanghai that accounted for about half of Tesla’s global deliveries last year.

Musk is also the CEO of rocket and satellite internet company SpaceX, among others.

Musk previously suggested that tensions between China and Taiwan could be resolved by handing over some control of Taiwan to Beijing. Musk also said China has sought assurances that he would not offer SpaceX’s Starlink internet service there.

He also proposed that Ukraine permanently cede Crimea to Russia, while saying SpaceX could not indefinitely fund Starlink services in Ukraine.

Ian Bremmer, the head of political-risk consultancy Eurasia Group, tweeted that Musk told him that he had spoken to Putin and the Kremlin directly about Ukraine. Musk denied his claims.

BBC