Former President Donald Trump has been summoned to testify before a U.S. congressional committee investigating last year's Capitol riot. Trump could risk criminal prosecution and imprisonment if he does not cooperate with the summons, known as a subpoena.

"He is required to answer for his actions," Representative Bennie Thompson, a Mississippi Democrat, said.

The select committee is investigating the Jan. 6, 2021 invasion of Congress by Trump loyalists. The decision to issue the subpoena on Thursday for the former Republican president to disclose records and evidence under oath in relation to the Capitol riot was approved 9-0 by the panel's seven Democrats and two Republicans.

The subpoena, which is anticipated to be released in the upcoming days, will provide a timetable by which Trump must comply or suffer consequences.

The unexpected move occurred during the ninth and likely final public session for the investigation into the raid on Congress last year.

The committee stated Thursday that it would focus on Trump's "state of mind" as he refuses to concede defeat to Joe Biden in the November 2020 presidential election.

Trump, who has slammed the investigation as a farce aimed to divert attention away from Democratic governance's "disaster" is generally likely to refuse to testify and fight the subpoena.

Over 1,000 witnesses, including Trump's children, key advisors, and top military and police officers, have been interviewed by the panel over the course of more than a year. The committee displayed never-before-seen images of Congress being evacuated as the building was invaded, and legislators being relocated to secure shelters during Thursday's session.

Steve Bannon, Trump's political advisor, disobeyed a similar legal summons from the select committee to testify, and he was found guilty of criminal contempt of Congress in July.

Speaker of the House Nancy Pelosi, a Democrat, is heard expressing disbelief when informed that lawmakers in another area of the building were being instructed to wear gas masks. Pelosi's daughter captured the incident on camera.

The committee also heard evidence indicating Trump was aware of his defeat but continued to promote the hoax that the election had been rigged despite it.

After the election, the president was reportedly watching the news when he addressed his communications director, Alyssa Farah, in testimony that was captured on camera:

"Can you believe I lost to this effing guy?"

Over 850 people have been charged for taking part in the riot at Congress.

The committee's rules require its members to produce a report on their findings. It is scheduled for release in December.