Ivanka Trump, one of her father's most trusted allies during his four years in the White House, appeared in a video deposition shown during the first in a series of congressional hearings by a House of Representatives select committee investigating the deadly attack on January 6, 2021.

"I respect attorney-general (William) Barr. So I accepted what he was saying," she told congressional investigators.

And what Barr was saying, Ivanka testified, was that his Justice Department had discovered no significant fraud to support Donald Trump's claim - one the former president is still making - that massive voter fraud in several key states caused the 2020 election to be "stolen" from him.

The committee showed a video of Barr's appearance before panel investigators. In that video, Barr called his former boss' fraud claims "bulls**t".

The former president has been more successful in persuading Republican voters of this view.

A Reuters/Ipsos poll completed on Wednesday found 58 per cent of Republicans viewed the outcome of the 2020 election to be the result of fraud.

Also shown testifying was Ivanka's husband Jared Kushner, another of the former president's top aides.

In the video, the president's son-in-law mentioned "whining", referring to top Trump aides threatening to resign because of the Jan 6 attack.

The riot followed shortly after Trump gave an incendiary speech to thousands of supporters outside the White House, repeating his false claims of a stolen 2020 election and urging them to march on the Capitol and "fight like hell".

Australian Associated Press