Washington DC - US President Joe Biden on Wednesday said that tech billionaire Elon Musk's relations with other countries were worthy of being scrutinized.

"I think that Elon Musk's cooperation and/or technical relationships with other countries is worthy of being looked at," Biden told reporters when asked whether Musk posed a threat to national security.

"Whether or not he is doing anything inappropriate, I am not suggesting that. I am suggesting that it's worth being looked at," Biden went on, without elaborating how that would work.

Musk is the chief executive officer of Tesla and SpaceX and has recently bought social media platform Twitter after months of back and forth in a $44-billion deal. He is considered one of the wealthiest people in the world.

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China is a very important market for Tesla, and the car manufacturer has a large factory there.

Saudi Prince Alwaleed bin Talal and his Kingdom Holding Company have become a major investor in Twitter since the Musk takeover. Crypto exchange company Binance, which was originally founded in China but has since moved its operations, invested $500 million in Musk's acquisition of Twitter.

The Washington Post earlier this month reported that the US Treasury Department had asked Twitter for more information about its ownership structure and Musk's agreements with foreign investors.

The newspaper cited experts as saying that the US government would probably be mostly concerned about whether foreign investors would have special access to Twitter users' personal data.

US authorities are particularly concerned about access to US data by third countries. The concerns have led Washington to take action against the popular video app TikTok, which belongs to Chinese group Bytedance.