WASHINGTON - A pair of former White House officials appeared in front of the House select committee investigating the Jan 6, 2021 attack on the US Capitol at a prime-time hearing Thursday night.

Former US deputy national security adviser Matthew Pottinger and former White House deputy press secretary Sarah Matthews provided testimony as investigators on the panel detailed what then President Donald Trump did throughout the violent event.

"I thought that Jan 6, 2021, was one of the darkest days in our nation's history and President Trump was treating it as a celebratory occasion," Matthews said. She and Pottinger were among a series of Trump administration officials who resigned that day in response to the Republican's actions.

The committee has held eight public hearings in June and July. Democratic Chairman of the congressional committee Bennie Thompson said there are more hearings to come in September.

Trump's allies and supporters have denounced the inquiry as a political "witch hunt" designed to undermine him and the Republican Party.

On Jan 6 last year, thousands of individuals, mostly Trump's supporters, stormed the Capitol in Washington, D.C. and disrupted a joint session of Congress in the process of affirming the 2020 presidential election results.

Approximately 140 police officers were assaulted in the Capitol attack, including about 80 US Capitol Police and 60 from the Metropolitan Police Department. Authorities have linked at least five deaths to the mayhem.

The worst attack on Congress in more than 200 years, the siege led to Trump's second impeachment by the House shortly before his term officially ended.