The US House of Representatives panel investigating the deadly attack on the US Capitol last January is seeking cooperation from Sean Hannity, the Fox News host and one of Donald Trump’s closest allies in the media, as the committee continues to widen its scope.

Congressman Bennie Thompson, the chair of the committee, and vice-chair Liz Cheney have requested that Hannity answer questions in relation to communications between Hannity and the former president, as well as the former president’s chief of staff Mark Meadows, and others in the days leading up to the attack, the day itself and in the aftermath.

In a letter to Hannity, made public on Tuesday, Thompson and Cheney wrote: “The Select Committee now has information in its possession, as outlined in part below, indicating that you had advance knowledge regarding President Trump’s and his legal team’s planning for January 6th.

“It also appears that you were expressing concerns and providing advice to the President and certain White House staff regarding that planning. You also had relevant communications while the riot was underway, and in the days thereafter. These communications make you a fact witness in our investigation.”

The House select committee investigating the 6 January insurrection revealed last month that Hannity and other Fox News hosts had messaged Meadows during the attack. Hannity has been a major supporter of Trump on his Fox show, as well as an adviser to the former president.

“Can he make a statement? Ask people to leave the Capitol?” Hannity texted Meadows during the attack, the recently released records show. The anchor has avoided publicly blaming Trump for riling up the crowd that then attacked the Capitol.

In his letter, Thompson said that the committee has “immense respect for the First Amendment to our Constitution, freedom of the press, and the rights of Americans to express their political opinions freely”, and did not intend to seek information regarding Hannity’s broadcasts.

However, the chairman said, the committee also has a responsibility to investigate the dozens of text messages it has in its possession, dating from 31 December 2020 to 20 January 2021, between Hannity, Trump and Meadows regarding the outcome of the 2020 presidential election and Trump’s failed efforts to contest it.

One specific December 2020 text from Hannity to Meadows highlighted in the letter reads: “I do NOT see January 6 happening the way he is being told. After the 6 th. (sic) He should announce will lead the nationwide effort to reform voting integrity. Go to Fl and watch Joe mess up daily. Stay engaged. When he speaks people will listen.”

The letter to Hannity also highlights texts from the night before the insurrection, including one in which Hannity said he was “very worried about the next 48 hours” and another to Meadows in which he wrote, “Pence pressure. WH counsel will leave.” The letter says it appears from other text messages that Hannity may have spoken directly with Trump on 5 January regarding planning for the following day.

Hannity had previously criticized the violence that took place nearly a year ago at the Capitol. But he’s also been sharply critical of the committee and its work, saying after his texts were revealed: “We’ve been telling you that this is a waste of your time and money. They have a predetermined outcome.”

A Fox News spokesperson declined to comment on the request. Jay Sekulow, Hannity’s lawyer, told the Associated Press on Tuesday night that they are reviewing the committee’s letter and “will respond as appropriate”.

The request is the first by the nine-member panel to a member of the media and opens a new door for the investigation as it widens its scope to any and all people who were in contact with the former president and his inner circle in the time surrounding the attack.

The committee says the extraordinary trove of material it has collected 35,000 pages of records so far, including texts, emails and phone records from people close to Trump is fleshing out critical details of the worst attack on the Capitol in two centuries, which played out on live television.

As the House prepares to commemorate the anniversary of the attack Thursday, the panel, which commenced its work last summer, has already interviewed nearly 300 people and issued subpoenas to more than 40 as it seeks to create a comprehensive record of the attack and the events leading up to it.

Thompson said about 90% of the witnesses called by the committee have cooperated despite the defiance of high-profile Trump allies such as Meadows and Steve Bannon.

Joe Biden and Kamala Harris will mark the anniversary this Thursday with speeches, alongside a slate of commemorative events.

On Monday, meanwhile, Donald Trump announced he was cancelling his own press conference on the day, blaming the House committee.

“In light of the total bias and dishonesty of the January 6th Unselect Committee of Democrats, two failed Republicans, and the Fake News Media, I am canceling the January 6th Press Conference at Mar-a-Lago,” Trump said.