WASHINGTON (REUTERS) - Longtime Donald Trump ally Steve Bannon could face criminal prosecution for refusing to cooperate with a probe into the deadly Jan 6 attack on the United States Capitol.

This came after the House of Representatives voted on Thursday (Oct 21) to hold him in contempt of Congress.

The Democratic-led chamber voted 229 to 202, with nine Republicans joining Democrats to recommend the charges against Mr Bannon, who served as chief strategist for the Republican former president.

US Attorney-General Merrick Garland will make the final decision on whether to prosecute.

Mr Bannon has refused to comply with subpoenas from the Jan 6 Select Committee seeking documents and his testimony, citing Mr Trump's insistence - disputed by some legal scholars - that his communications are protected by the legal doctrine of executive privilege.

"What sort of precedent would it set for the House of Representatives if we allow a witness to ignore us flat out without facing any consequences?" Democrat Bennie Thompson, chairman of the Select Committee, said in debate before the vote.

The select committee voted unanimously on Tuesday in favour of the charges.

The Democratic-led panel hopes the threat of jail time - contempt of Congress carries a penalty of up to one year in prison and a US$100,000 (S$134,650) fine - will encourage cooperation from the 18 other Trump aides and rally organisers who also have been subpoenaed.

Mr Garland has yet to indicate how the department will respond.

He told a House Judiciary Committee hearing on Thursday that the department would "apply the facts and the law" and make decisions "consistent with the principles of prosecution".

Most of Mr Trump's fellow Republicans in Congress opposed creating either an independent commission or a select committee to investigate the events surrounding Jan 6. That day thousands of Trump supporters descended on the Capitol after he urged them in a fiery speech to protest his defeat by Democrat Joe Biden in a November 2020 election that Mr Trump falsely claims was stolen.

Only two Republicans - Representatives Liz Cheney and Adam Kinzinger - are on the nine-member select committee.

They were joined by seven other Republicans in backing the House contempt resolution. Representative Greg Pence, whose brother, former vice-president Mike Pence, was forced to flee from the crowds on Jan 6, did not vote.

A spokesman said later Mr Mike Pence had a family medical emergency and would have voted no.

Most of the Republicans who voted to hold Mr Bannon in contempt also voted earlier this year to impeach Mr Trump over the Jan 6 riot.

The contempt of Congress statute, passed in 1857, states that the Justice Department has a duty to bring a House contempt citation before a grand jury.

But the Justice Department historically has said it makes the ultimate decision about whether to prosecute individuals who defy congressional subpoenas. The last successful prosecution for contempt of Congress was in 1974 when a judge found Watergate conspirator G. Gordon Liddy guilty.

Arguing against the resolution in the House, Republican Representative Jim Banks accused the committee of political motives for pursuing Mr Bannon, who played a major role in Mr Trump's 2016 election victory.

"Steve Bannon was a private citizen before, after and during Jan 6. So why is the select committee interested in Steve Bannon? It's simple. He's a Democrat party bogeyman," Mr Banks said.

Four people died on the day of the assault, and one Capitol police officer died the next day after being injured while defending the seat of government. Hundreds of police officers were injured and four have since taken their own lives.

The select committee argued that Mr Bannon had made statements suggesting he knew ahead of time about "extreme events" that would take place on Jan 6, when Congress was scheduled to certify Mr Biden as the winner of the presidential election.

Mr Bannon said on a Jan 5 podcast that "all hell is going to break loose tomorrow". The next day, mobs of Trump supporters, many chanting "Stop the Steal" and "Hang Mike Pence", attacked the Capitol as Mr Pence and lawmakers met to certify the election.

"Mr Bannon's own public statements make clear: he knew what was going to happen before it did... The American people deserve to know what he knew, and what he did," Ms Cheney, who is vice-chairman of the Select Committee, said during debate.

The assault forced members of Congress, staff and journalists to flee as crowds rampaged through the building, vandalising offices and hallways, smashing windows and stealing computers and other equipment.

Mr Trump has continued to insist falsely that his defeat was the result of fraud. Multiple courts, state election officials and members of Mr Trump's own administration have rejected that claim.