Former US President Donald Trump has decried the congressional probe into the riot by his supporters last year at the US Capitol as a "mockery of justice".

In a rambling, 12-page statement, Mr Trump said that instead of focusing on the country's larger problems, the Democratic-led panel was "a Kangaroo Court, hoping to distract the American people from the great pain they are experiencing".

The former president also reiterated the same conspiracy theories about the 2020 presidential election that the congressional probe had earlier argued were a key motivating factor for his supporters to riot.

"Democrats created the narrative of January 6th to detract from the much larger and more important truth that the 2020 election was rigged and stolen," Mr Trump said in the statement.

He added that the panel "is making a mockery of justice".

The congressional panel - comprised of seven Democrats and two Republicans - showed videos in which former aides to Mr Trump testified that they repeatedly told the president that his assertions of widespread fraud in the election were false.

"When I went into this and would tell him how crazy some of these allegations were, there was never an indication of interest in the actual facts," former US attorney general Bill Barr said in testimony.

He likened addressing Mr Trump's avalanche of false allegations with playing the game "whack-a-mole".

"I was demoralised because I thought, boy ... he's become detached from reality if he really believes this stuff," Mr Barr said.

The committee ended its hearing with video of Trump supporters on 6 January 2021 repeating his theories of fraud in the election, shortly before a mob descended on the Capitol.

But Mr Trump doubled down on his debunked election lie in his statement.

"The truth is that Americans showed up in Washington, DC in massive numbers ... on January 6th, 2021, to hold their elected officials accountable for the obvious signs of criminal activity throughout the election," Mr Trump said.