US media outlets, citing Secret Service sources, said the head of Trump's security detail, Robert Engel, and the driver of the car were prepared to challenge the aide's testimony that Trump grabbed the steering wheel of the modified Chevrolet Suburban when he learned that the Secret Service would not drive him to the Capitol, where thousands of his supporters rioted.

Neither Engel nor the driver made public statements on Wednesday.

Trump on Tuesday denied having grabbed the wheel.

An aide to the US House of Representatives committee on January 6 said it would welcome testimony from any witness who wished to provide new information under oath following Tuesday's testimony by Cassidy Hutchinson, an aide to Trump's White House Chief of Staff Mark Meadows.

The House aide on Wednesday declined to answer questions about whether the committee already had interviewed Secret Service agents or other officials with first-hand knowledge of the incident Hutchinson described.

Secret Service spokesman Anthony Guglielmi said on Wednesday the committee had not sought to confirm details of Hutchinson's testimony in the 10 days before the hearing, which was scheduled unusually quickly.

In a separate statement it said it was co-operating with the committee.

Guglielmi did not immediately respond to questions about the significance of the 10 days or whether the committee contacted the agency previously to discuss Trump's January 6 behaviour.

Hutchinson testified that Tony Ornato, a senior Secret Service official, told her that Trump had struggled with agents after giving a fiery speech to his supporters outside the White House that morning in which he repeatedly blamed widespread fraud for his election loss to Joe Biden.

Trump's claims of voting fraud have been dismissed by a succession of judges and rejected by state election officials.

The riot was an attempt to stop Congress, with vice president Pence presiding, from certifying Biden's election.

"If it is true the Secret Service denies the allegations against President Trump of lunging and assaulting officers, then the story is really passing along gossip that did not bear fruit," Republican US Senator Lindsey Graham said on Wednesday.

"The committee, with a little bit of effort, could have told the other side of the story but they chose NOT to because they wanted sensational headlines."

Supporters of the Republican Trump have not challenged other revelations in Hutchinson's testimony.

These included Trump's knowledge - even approval - of his supporters walking around Washington DC heavily armed on January 6 and that he had no qualms about rioters urging that Pence be hanged.

Hutchinson also testified that Trump was known for angry outbursts in the White House that left food being splayed onto walls and dishes upended.

"Cassidy Hutchinson's testimony before the January 6 Committee has been praised as 'courageous' and dismissed as 'unbelievable,'" said Democratic Senator Dick Durbin on Twitter on Wednesday.

"It's time for those present for some of the darkest moments for our democracy to come forward under oath and, like her, tell their stories."

As Meadows' former deputy, Hutchinson, now 26, was a constant presence among White House staff in the last several months of 2020, frequently flying aboard Air Force One, friendly with staff and with Trump's Secret Service detail.

Her office was a 10-second walk from the president's Oval Office.

Aides who worked at the White House were surprised at the outsized influence for a then-24-year-old and surprised at her tale of drama on the SUV the day of the riot.

Sources familiar with the matter said she had planned to join the small contingent of staffers who moved to Florida with Trump after he handed over power to Biden in January 2021 but Trump ultimately opted not to hire her.

Australian Associated Press