Former US president Donald Trump has belittled a witness who made startling revelations in testimony to the House panel investigating the US Capitol attack.

Displaying deep frustration, Mr Trump called the 26-year-old ex-White House staffer Cassidy Hutchinson a no-name junior aide and a liar.

“For this girl to just make up stories …,” said Mr Trump, whose voice trailed off in an interview that aired Thursday on the far right-wing Newsmax network.

“She has serious problems … mental problems,” Mr Trump added.

The attacks marked a new low in Mr Trump’s offensive against Ms Hutchinson, who rocked the nation with her testimony about the former president’s bizarre and erratic behaviour.

Mr Trump made it clear the panel had got deeply under his skin, complaining it has been given free rein to discuss his misdeeds indefinitely.

“How long is this going to go on for?” he said.

He broadly accused Ms Hutchinson of lying and committing perjury by relating several of his statements and actions on January 6, 2021.

“It was totally false,” he said. “And that a person can totally get away with it.”

But Mr Trump pointedly did not challenge Ms Hutchinson’s specific testimony about two key points: That he knew the MAGA crowd was illegally armed when he pleaded with them to keep him in power and that he angrily tried to get Secret Service agents to take him to the Capitol to lead the attempted insurrection.

Ms Hutchinson testified under oath that she heard officials tell Mr Trump that many in the crowd of his supporters were armed and that they refused to go through metal detectors because they feared Secret Service agents would strip them of the knives and illegal guns.

Mr Trump denied only urging supporters to carry weapons, an issue Ms Hutchinson never addressed in her Tuesday testimony.

“I didn’t encourage people to have guns,” Mr Trump said.

“I’m one of the speakers. I wouldn’t want people to have guns for me either.”

The former president mocked Ms Hutchinson’s claim that he tried to “commandeer” the presidential limousine or that he wanted to “strangle” his lead Secret Service agent.

But Ms Hutchinson was relating under oath what Mr Trump loyalist Tony Ornato told her minutes after the incident and did not claim to have witnessed it.

Secret Service agents have confirmed that Mr Trump angrily demanded to be taken to the Capitol. They have denied the allegation that he sought to grab the steering wheel and physically attacked an agent.

But neither Mr Ornato nor any agents have testified under oath nor specifically denied Ms Hutchinson’s account that Mr Ornato told her about the incident.