US President Joe Biden Wednesday said that Elon Musk's ties with foreign countries were "worthy" of scrutiny, amid questions over the Saudi acquisition of a stake in Twitter as part of the tycoon's blockbuster takeover.

"I think that Elon Musk's cooperation and/or technical relationships with other countries is worthy of being looked at," Biden said, answering a question from a reporter after a long pause.

"Whether or not he is doing anything inappropriate, I'm not suggesting that... That's all I'll say," he said.

Last month reports emerged that the Biden administration was weighing a national security review of Musk's $44 billion takeover of Twitter, in part because of a key group of investors backing the buyout.

The investors include Prince Alwaleed bin Talal of Saudi Arabia and Qatar's sovereign wealth fund.

Two US Senators have called for a vetting of the Twitter deal in order to prevent the platform from accessing user information that could endanger human rights activists and critics of the Saudi government.

"We should be concerned that the Saudis, who have a clear interest in repressing political speech and impacting US politics, are now the second-largest owner of a major social media platform," said Senator Chris Murphy of Connecticut.

Musk has also struck what's seen as a favorable public posture towards Vladimir Putin despite Russia's invasion of Ukraine -- notably by echoing the Russian president's talking points on the conflict.

And he has raised eyebrows by suggesting the self-ruled island of Taiwan should become part of China -- a stance welcomed by Chinese officials but which deeply angered Taiwanese officials.

Critics point to the industrial ties linking Musk to China, which has increasingly fraught ties with Washington.

The tycoon's Tesla electric auto company has ramped up production to record levels at its Chinese factory in Shanghai.