Elon Musk, the world's richest man and an avid supporter of Donald Trump, was plunged into new controversy on Friday after a report that he is in regular contact with Russian President Vladimir Putin.

The Wall Street Journal story, which has been denied by the Kremlin, comes days after the U.S. Justice Department sent a letter to Musk's America PAC warning that its $1 million giveaways to registered voters may violate federal law.

Musk, 53, the chief executive of SpaceX and Tesla and the owner of X, formerly Twitter, has thrown his millions, time and considerable influence into sending the former Republican president back to the White House since endorsing him in July.