WASHINGTON, United States (AFP) -- Billionaire Elon Musk sparked controversy Monday after making a gesture at an event celebrating US President Donald Trump’s inauguration, with some calling it a “Nazi” or “fascist” movement.

The X, SpaceX and Tesla chief appeared on stage at the Capital One Arena in Washington, where supporters of the newly inaugurated president had gathered for a rally.

Upon thanking the crowd for returning the 78-year-old Republican to the White House, Musk tapped the left side of his chest with his right hand and then extended his arm with his palm open, repeating the gesture for the crowd seated behind him.

Claire Aubin, a historian who specializes in Nazism within the US, agreed Musk’s gesture was a “sieg heil,” or Nazi salute.

“My professional opinion is that you’re all right, you should believe your eyes,” Aubin posted on X, aligning with those who found the gesture was an overt reference to Nazis.

Musk later posted on X that his opponents needed “better dirty tricks.”

“The ‘everyone is Hitler’ attack is sooo tired,” he said.

Ruth Ben-Ghiat, a historian of fascism, also found the gesture “was a Nazi salute — and a very belligerent one too,” she said on X.

Democratic Party members also quickly responded with alarm.

Congressman Jimmy Gomez reacted to the moment by posting on X: “Well, that didn’t take long.”

One attendee at the rally told Agence France-Presse he thought Musk was making the gesture as a joke.

“He’s very humorous, and he uses a lot of sarcasm. So when he did that on the stage, I don’t think he meant it,” said Brandon Galambos, a 29-year-old pastor and tech worker.

Reports by Wired and Rolling Stone magazines said far-right personalities in the US were celebrating the move, like the writer Evan Kilgore, who called the salute “incredible.”

The Anti Defamation League (ADL), an organization founded to combat anti-Semitism which has criticized Musk in the past, defended his actions this time around.

“It seems that Elon Musk made an awkward gesture in a moment of enthusiasm, not a Nazi salute,” the organization said in a statement posted on X.

Democratic Representative Alexandria Ocasio-Cortez blasted the ADL’s reaction, saying on X: “Just to be clear, you are defending a Heil Hitler salute that was performed and repeated for emphasis and clarity.”

Another historian, Aaron Astor, also rebuffed accusations of Musk’s Nazi emulation.

“I have criticized Elon Musk many times for letting neo-Nazis pollute this platform,” he wrote on X, adding: “But this gesture is not a Nazi salute.”