French far-right leader Jordan Bardella cancelled a planned speech at the Conservative Political Action Conference in Washington, after Donald Trump's former top adviser made a hand gesture on stage that Bardella and others likened to a Nazi salute.

Steve Bannon yelled "fight, fight, fight" before extending his right arm, fingers pointed and palm down, during his CPAC speech on Thursday evening.

Bardella, who leads France's National Rally party, was already in Washington and had been scheduled to speak at the event on Friday. He said in a statement that he was cancelling his appearance over what he called a "gesture referring to Nazi ideology".

Bannon denied the Nazi comparison and called the gesture a "wave", saying it was the "exact same wave" he did on stage at a speech seven years ago in France to Bardella's party.

"If he cancelled [the speech] over what the mainstream media said about the speech, he didn't listen to the speech. If that's true, he's unworthy to lead France. He's a boy, not a man," Bannon told the French news magazine Le Point.

Bannon's onstage hand gesture appeared to mirror one from tech billionaire-turned-presidential adviser Elon Musk during Donald Trump's inauguration in January. Musk also denied he had performed a Nazi salute after an uproar.

Bardella, seen as a future French presidential hopeful, was one of several high-profile international politicians scheduled to speak at CPAC during the four-day conference, which began on Wednesday.

Former UK Prime Minister Liz Truss addressed the conservative bash on its first day, telling attendees that the British state was "failing". On Thursday, Argentine President Javier Milei handed Elon Musk a shiny chainsaw that he wielded on stage, celebrating sweeping cuts to the federal government by his Doge initiative.

Italian Prime Minister Giorgia Meloni is due to speak on Saturday, ahead of President Trump's address.

The annual CPAC conference has become increasingly dominated by Trump's Make America Great Again movement, and this year, it has taken on a celebratory tone in the wake of his election victory in November.

Speaker after speaker have lauded the blizzard of action launched by the White House in the month since the Republican returned to the Oval Office.

Bannon was met with a standing ovation after his speech on Thursday, which ended with the controversial gesture.

"The only way that they win is if we retreat, and we are not going to retreat," he told the crowd.

"We're not going to surrender, we are not going to quit, we're going to fight, fight, fight."

Bannon was Trump's top adviser at the start of his first term in office before the president fired him. The firebrand conservative hosts the influential War Room podcast, listened to by legions of Trump supporters.

He was released from prison in October, after serving four months for defying a congressional subpoena over the attack on the US Capitol on 6 January 2021.