The House panel investigating the January 6 insurrection at the US Capitol have laid the blame firmly on former president Donald Trump.

The committee said the assault was not spontaneous but an "attempted coup" and a direct result of the defeated president's effort to overturn the 2020 election.

With a never-before-seen 12-minute video of the deadly violence and testimony from Mr Trump's most inner circle, the House committee said the former president's repeated lies about election fraud and his public effort to stop Joe Biden's victory led to the attack and imperilled American democracy.

"Democracy remains in danger," said congressman Bennie Thompson, chairman of the panel, during the hearing.

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

In a previously unseen video clip, the panel played a quip from former attorney general Bill Barr who testified that he told Mr Trump the claims of a rigged election were "bull****".

In another, the former president's daughter, Ivanka Trump, testified to the committee that she respected Mr Barr's view that there was no election fraud.

Others showed leaders of the extremist Oath Keepers and Proud Boys preparing to storm the Capitol to stand up for Mr Trump.

Testifying in person was one of the police offices, Caroline Edwards, who suffered serious injuries as she battled the mob that pushed into the Capitol.

"President Trump summoned a violent mob," said congresswoman Liz Cheney, the panel's vice chair who took the lead for much of the hearing.

"When a president fails to take the steps necessary to preserve our union - or worse, causes a constitutional crisis - we're in a moment of maximum danger for our republic."

There was an audible gasp in the hearing room, when Ms Cheney read an account that said when Mr Trump was told the Capitol mob was chanting for vice president Mike Pence to be hanged, Mr Trump responded that maybe they were right, that he "deserves it".

Mr Trump was angry that Mr Pence, presiding in the House chamber, refused his order to reject the certification of Mr Biden's victory.

Police officers who had fought off the mob consoled one another as they sat in the committee room reliving the violence they faced on January 6. Officer Harry Dunn began to cry as bodycam footage showed rioters bludgeoning his colleagues with flagpoles and baseball bats.

Mr Biden, in Los Angeles for the Summit of the Americas, said many viewers were "going to be seeing for the first time a lot of the detail that occurred".

Mr Trump, unapologetic, dismissed the investigation anew - and even declared on social media that January 6 "represented the greatest movement in the history of our country".

Republicans on the House Judiciary Committee tweeted: "All. Old. News."

The riot left more than 100 police officers injured, many beaten and bloodied, as the crowd of pro-Trump rioters, some armed with pipes, bats and bear spray, charged into the Capitol. At least nine people who were there died during and after the rioting, including a woman who was shot and killed by police.

Among those testifying was documentary maker Nick Quested, who filmed the Proud Boys storming the Capitol - along with a pivotal meeting between the group's then-chairman Henry "Enrique" Tarrio and the Oath Keepers the night before in a nearby parking garage.

Court documents show members of the Proud Boys and Oath Keepers were discussing as early as November a need to fight to keep Mr Trump in office. Leaders of both groups and some members have since been indicted on rare sedition charges over the military-style attack.

In the weeks ahead, the panel is expected to detail Mr Trump's public campaign to "Stop the Steal" and the private pressure he put on the Justice Department to reverse his election loss - despite dozens of failed court cases and his own attorney general saying there was no fraud on a scale that could have tipped the results in his favour.

The hearings are expected to introduce Americans to a cast of characters, some well-known, others elusive, and to what they said and did as Mr Trump and his allies tried to reverse the election outcome.

The public will learn about the actions of Mark Meadows, the then president's chief of staff, whose 2,000-plus text messages provided the committee with a snapshot of the real-time scramble to keep Mr Trump in office.

The US Justice Department has arrested and charged more than 800 people for the violence that day.