The congressional panel investigating the attack on the US Capitol has taken aim at a fellow lawmaker as it released video footage showing him giving a tour of the building the previous day to a man involved in the riot.

The video shows the man in question, who was not named, taking pictures of tunnels and security checkpoints the day before the insurrection during a guided tour by Republican representative Barry Loudermilk.

Separate footage released by the House of Representatives panel shows the man issuing threats to prominent Democrats as he approached the Capitol on January 6, 2021, with thousands of other supporters of then-president Donald Trump.

Mr Loudermilk’s office accused the committee of a “smear campaign” and cited a letter from the Capitol Police saying that the activity of the tour group was not suspicious.

That letter said the group was not seen in tunnels that led to the Capitol and there was no evidence that Mr Loudermilk entered the Capitol with them during their visit.

The committee chair, Democratic representative Bennie Thompson, said the behaviour of the group raised questions because they photographed security checkpoints and other areas that were not typically of interest to tourists on a day when the Capitol complex was closed to the public.

The committee said it had repeated a request to Mr Loudermilk to provide information.

The request comes amid heightened tension between the Democratic-led committee and most Republican House members, who have removed the top Republican on the committee, Liz Cheney, from a leadership post.

Committee members said at a hearing last week that more than one congressional Republican had asked Mr Trump for a pardon, drawing a sharp denial from Representative Scott Perry, the only one named.

The video shown on Wednesday includes clips apparently taken on the man’s mobile phone as he narrated, as well as surveillance footage from the Capitol complex on January 5 showing him taking pictures of staircases, security checkpoints and tunnels not normally of interest to tourists.

In the video, the man is heard threatening high-profile Democratic lawmakers, including House Speaker Nancy Pelosi and Senate Majority Leader Chuck Schumer.

“They are swarming and converging… from all routes in. There’s no escape… We’re coming for you,” the man said as he approached the Capitol according to a video released by the House of Representatives committee.

It was not clear if the man was among the more than 840 people charged with taking part in the riot.

The committee is holding at least six public hearings this month on the findings of its nearly year-long probe.

After the third hearing was postponed on Wednesday, a senior aide and a retired federal judge who advised former US vice-president Mike Pence are set to testify on Thursday.

The hearing will focus on Mr Pence’s role that day in overseeing formal congressional certification of Joe Biden’s 2020 election victory over Mr Trump, who has made false claims that the election was stolen through widespread voting fraud.

– AAP