Kupec said Mueller and Barr then discussed “whether additional context from the report would be helpful and could be quickly released”, but that the attorney general decided it would be counterproductive to release the report in “piecemeal fashion”.

It was after their conversation, she noted, that Barr released a second letter to Congress saying his first assessment was not intended to be a summary of Mueller’s report.

Barr, who is set to begin two days of testimony before Congress on Wednesday, has vigorously defended his framing of Mueller’s conclusions amid intense scrutiny over his conduct.

Earlier on Tuesday, Senate Democrats called on the Justice Department’s watchdog to independently investigate Barr’s handling of the Mueller report and “whether he has demonstrated sufficient impartiality” to continue overseeing 14 ongoing criminal matters related to the special counsel’s investigation.

Mueller concluded the two-year investigation into Russian interference in the 2016 presidential election last month and subsequently delivered a final report to Barr spanning more than 400 pages.

Barr initially released a letter on 24 March citing Mueller’s conclusion that there was no criminal conspiracy between the Trump campaign and Moscow. Barr also declared in the same letter that he did not believe there was sufficient evidence to charge Trump with obstruction of justice.

But a redacted version of Mueller’s report, which was made public on 18 April, revealed nearly a dozen instances in which the president sought to obstruct the investigation. The report also stated that the Trump campaign was “receptive” to assistance from Moscow during the 2016 election and expected to benefit from Russian interference.

Barr nonetheless delivered a press conference, prior to his public release of the redacted report, that essentially sought to absolve the president of wrongdoing. In his statement, Barr repeatedly echoed Trump’s claims of “no collusion” with the Russians and downplayed the president’s attempts to impede the special counsel investigation.

House Democrats have issued a subpoena for the full Mueller report and underlying evidence, setting the stage for what is expected to be a protracted legal battle with the Justice Department and the White House.