Supporters of US President Donald Trump protest outside the US Capitol on Wednesday, in Washington, DC. Demonstrators breached security and entered the Capitol as Congress debated the 2020 presidential election Electoral Vote Certification. Photo: AFP

A US congressional committee probing the deadly January 6 assault on the Capitol voted unanimously on Tuesday in favor of contempt-of-Congress charges against Steve Bannon, a longtime aide to former president Donald Trump.

The seven Democratic and two Republican members of the House of Representatives Select Committee approved a report recommending the criminal charge by a 9-0 vote, calling it "shocking" that Bannon refused to comply with subpoenas seeking documents and testimony.

Approval of the report paved the way for the entire House to vote on whether to recommend contempt charges. That vote is set for Thursday, when the full, Democratic-controlled chamber is expected to approve the report.

A spokesperson for the US Attorney's Office for the District of Columbia said prosecutors there would "evaluate the matter based on the facts and the law" if the full House approves the recommendation.

"It's a shame that Mr Bannon has put us in this position. But we won't take 'no' for an answer," Representative Bennie Thompson, the panel's chairman, said in his opening remarks.

Bannon's attorney did not respond to a request for comment on Tuesday evening.

Before leaving office in January, Trump pardoned Bannon of charges he had swindled the Republican president's supporters. Trump has urged former aides subpoenaed by the panel to reject its requests, claiming executive privilege.

Bannon has said he will not cooperate with the committee until Trump's executive privilege claim is resolved by a court or through a settlement agreement.

At Tuesday's meeting, Republican Representative Liz Cheney, the select committee's vice chair, said: "Mr Bannon's and Mr Trump's privilege arguments do appear to reveal one thing, however: They suggest that president Trump was personally involved in the planning and execution of January 6. And we will get to the bottom of that."

Thompson said Bannon "stands alone" among those subpoenaed in his refusal to cooperate.

More than 670 people have been charged with taking part in the riot, the worst attack on the US government since the War of 1812. The select committee has issued 19 subpoenas.

"It's shocking to me that anyone would not do everything in their power to assist our investigation," Thompson said.

In its report, the committee argued that Bannon made statements suggesting he knew ahead of time about "extreme events" on January 6, when Congress was scheduled to certify Democrat Joe Biden as the winner of the presidential election.

Bannon said on a January 5 podcast that "all hell is going to break loose tomorrow." The next day, thousands of Trump supporters descended on the Capitol.

Four people died on the day of the assault, and one Capitol police officer died the next day of injuries sustained in defense of the seat of Congress. Hundreds of police officers were injured and four have since taken their own lives.

Trump filed suit on Monday, alleging the committee made an illegal, unfounded and overly broad request for his White House records, which committee leaders rejected.

Reuters