Steve Bannon, an architect of Donald Trump's 2016 election victory, was arrested on a yacht on Thursday and pleaded not guilty after he was charged with defrauding donors in a scheme to help build the president's signature wall along the U.S.-Mexico border.

Bannon, 66, was among four people arrested and charged by federal prosecutors in Manhattan with conspiracy to commit wire fraud and conspiracy to commit money laundering.

A top adviser to Trump's presidential campaign who later served as White House chief strategist, Bannon helped articulate the "America First" right-wing populism and fierce opposition to immigration that have been hallmarks of Trump's 3-1/2 years in office. Trump fired Bannon from his White House post in August 2017.

Investigators allege that the group of conservative officlas defrauded donors, which led to raising "more than 25 million U.S. dollars to build a wall along the southern border of the United States."

Prosecutors claim the defendants "collectively received hundreds of thousands of dollars in donor funds from 'We Build the Wall,' which they each used in a manner inconsistent with the organization's public representations," according to the indictment.

The four people each face up to 40 years in prison if convicted, but would likely get much shorter sentences.

A handcuffed Bannon wore a protective white mask amid the coronavirus pandemic and two open-collared shirts when he appeared in federal court in Manhattan, where his lawyer entered a plea of not guilty on his behalf. He was freed on a five million U.S. dollars bond and barred from traveling internationally by a federal magistrate judge.

On leaving the courthouse, Bannon took off his mask and briefly addressed reporters before leaving in a black SUV.

"This entire fiasco is to stop people who want to build the wall," Bannon said.

Bannon was arrested in Connecticut by agents from the prosecutor's office and the U.S. Postal Inspection Service aboard a 150-foot-long (45-metre-long) yacht, according to a law enforcement source. That yacht, called the Lady May, is owned by Chinese fugitive billionaire Guo Wengui, with whom Bannon has had a working relationship.

The famously disheveled entrepreneur headed the right-wing Breitbart News website - a voice for the alt-right movement that spans hardcore nationalists, white supremacists, neo-Nazis and anti-Semites - before joining Trump's campaign. Bannon, an anti-globalist, has since promoted a variety of right-wing causes and candidates in the U.S. and abroad.

Trump told reporters at the White House that he felt "very badly" about the charges, but sought to distance himself from Bannon and the alleged scheme.

"I do think it's a sad event," Trump said. "I haven't dealt with him at all now for years, literally years."

Trump said he knew little about the project. But one of those involved, former Kansas Secretary of State Kris Kobach, said in 2019 that Trump had offered his support, according to the New York Times.

Bannon is the eighth close Trump associate to be arrested or convicted of a crime, a list that also includes former campaign chairman Paul Manafort, longtime friend and adviser Roger Stone, former national security adviser Michael Flynn and former personal lawyer Michael Cohen.

Trump has struggled to build his border wall - a key 2016 campaign promise - in the face of court challenges, logistical hurdles and congressional opposition. His administration has completed 48 kilometers of border fencing and replaced an additional 386 km of barriers along the 3,200-km border, government figures show.

"I know nothing about the project," Trump said on Thursday, "other than ... when I read about it, I didn't like it. I said, 'This is for government, this isn't for private people,' and it sounded to me like showboating."

Trump also said he did not believe he had ever met the three others charged.