By Richard Cowan and Moira Warburton

WASHINGTON (Reuters) -A U.S. congressional committee began a hastily called hearing into the January 6, 2021, assault on the U.S. Capitol by then- President Donald Trump's supporters, summoning a former White House aide to testify with new evidence.

The House of Representatives committee, investigating the first attempt to prevent the peaceful transfer of power in U.S. history, took two hours of testimony from Cassidy Hutchinson, an aide to Mark Meadows, then Trump's chief of staff.

Committee chairman Bennie Thompson previewed th new evidence "dealing with what was going on in the White House on January 6 and the days prior" to the riot at the Capitol.

Thompson praised Hutchinson's "courage" in coming forth to testify to the committee.

Hutchinson said Tuesday that Trump knew his supporters were armed while heading to the Capitol, but seemed unconcerned about his own safety.

“I was part of a conversation — I was in, I was in the vicinity of a conversation — where I overheard the president say something to the effect of: ‘You know, I don’t even care that they have weapons. They’re not here to hurt me,’” she recalled.

Sbe said Trump repeatedly expressed a desire to go to the Capitol after his speech on January 6. Hutchinson testified she first heard Trump attorney Rudy Giuliani raise the idea and was part of several conversations about it leading up to January 6. Among those who were opposed, she said, was White House counsel Pat Cipollone, who told her on January 3 or 4 that it would be a bad idea and that he had legal concerns about it.

As she set out to hear Trump’s speech on the Ellipse on January 6, Cipollone pulled her aside, Hutchinson recalled. “We’re going to get charged with every crime imaginable if we make that movement happen,” she said Cipollone told her. She testified that he feared the possibility of charges such as obstruction and inciting a riot.

In video testimony during the last hearing last week, Hutchinson told the committee that Republican allies of Trump had sought White House pardons after supporting his attempts to overturn his 2020 election defeat.

Testimony at the committee's five prior hearings has shown how Trump, a Republican, riled thousands of supporters with false claims that he lost the 2020 election to Democrat Joe Biden because of massive voter fraud.

The committee had said last week it would only reconvene publicly in July but announced a change of plans on Monday, a mere 24 hours before the start of Tuesday's hearing.

British filmmaker Alex Holder, who spent time filming Trump and his family in the weeks after the election, has in recent days testified before the committee behind closed doors and shared video of interviews he did with Trump and his family.

The committee has said it intends at some point to interview Virginia "Ginni" Thomas, wife of Supreme Court Justice Clarence Thomas, following reports she may have been involved in efforts to stop Biden's victory certification at the Capitol on Jan. 6. She has said she intends to speak to the panel.

Law enforcement agents last week raided the home of Jeffrey Clark, a former Justice Department official, who was an enthusiastic supporter of Trump's false fraud claims.

This month's hearings featured videotaped testimony from figures including Trump's oldest daughter, Ivanka Trump, and his former attorney general, Bill Barr. They and other witnesses testified that they did not believe Trump's false claims of widespread fraud and tried to dissuade him of them.

Dozens of courts, election officials and reviews by Trump's own administration rejected his claims of fraud, including outlandish stories about an Italian security firm and the late Venezuelan President Hugo Chavez tampering with U.S. ballots.

Trump, who is publicly flirting with another White House run in 2024, denies wrongdoing and accuses the committee of engaging in a political witch hunt. He has leveled harsh criticism particularly at Representative Liz Cheney, one of just two Republicans on the nine-member committee.

A Reuters/Ipsos poll early this month found that about two-thirds of U.S. Republicans believed Trump's false election fraud claims.

The committee, sometime next month, is expected to hold one or two hearings on possible coordination of the Jan. 6 attack by right-wing extremist groups.

During the assault on the Capitol, thousands of Trump supporters smashed windows, fought with police and sent lawmakers, including Trump's vice president, Mike Pence, fleeing for their lives.

Four people died the day of the attack, one fatally shot by police and the others of natural causes. More than 100 police officers were injured, and one died the next day. Four officers later died by suicide.

(Reporting by Richard Cowan and Moira Warburton, additional reporting by Doinad Chiacu and Rose Horowitch; editing by Scott Malone and Howard Goller)