WASHINGTON－A congressional panel investigating last year's mob assault on the United States Capitol laid out its case on Thursday that Donald Trump and his claims of a stolen election were at the heart of what amounted to an "attempted coup" to remain in power.

In a prime-time presentation of its findings from a yearlong probe, the special committee sought to persuade a divided country of the existence of a deep-rooted and ongoing plot orchestrated by the former president to overturn the result of the 2020 election won by Joe Biden.

"President Trump summoned the mob, assembled the mob and lit the flame of this attack," said Liz Cheney, the Republican vice-chairwoman of the panel, in her opening remarks in the first of a series of hotly anticipated summer hearings.

Minutes earlier, Democratic committee chief Bennie Thompson accused Trump of being "at the center of this conspiracy".

"Jan 6 was the culmination of an attempted coup－a brazen attempt, as one rioter put it shortly after Jan 6－to overthrow the government. The violence was no accident," he said.

Rioters acted "at the encouragement of the president of the United States", to march on Congress and block the formal transfer of power by lawmakers to Biden, he added.

The panel's carefully produced presentation made use of testimony given behind closed doors by some of Trump's most senior and trusted advisers, including former attorney general William Barr and Trump's son-in-law and senior aide Jared Kushner.

'Witch hunt'

The panel aims to demonstrate that the violence was part of a broader－and ongoing－drive by Trump and his inner circle to illegitimately cling to or regain power, tearing up the Constitution and more than two centuries of peaceful transitions from one administration to the next.

Thursday's session and five subsequent hearings over the coming weeks will focus on Trump's role in the multipronged effort to return him to the Oval Office by disenfranchising millions of voters.

Trump has defiantly dismissed the probe as a baseless "witch hunt". On his social media platform on Thursday, he defended the insurrection as "the greatest movement in the history of our Country to Make America Great Again".

Following the hearing, he lashed out again on Truth Social, accusing the committee of bias and doubling down on his election fraud claims.

"The Unselect Committee of political HACKS refuses to play any of the many positive witnesses and statements," he wrote.

Some congressional Republicans in the days after the attack condemned Trump, but most have since changed their tune, supporting him and downplaying the day's violence. Trump himself has gone after Republicans who voted to impeach him for his actions, backing primary challengers to them ahead of the Nov 8 midterm elections that will determine control of Congress for the following two years.

A Reuters/Ipsos poll released on Thursday underscored the partisan lens through which many people in the US view the assault. It found that among Republicans, about 55 percent believed the false claim that left-wing protesters led the attack and 58 percent believed most of the protesters were law-abiding.