Attorney General Jeff Sessions heatedly denied having an undisclosed meeting with Russia's ambassador to the US and declared it was a "detestable and appalling lie" to suggest he was aware of or took part in any collusion between Russia and the election campaign that sent Donald Trump to the White House.
Testifying at a packed Senate hearing, Sessions, who was a close Trump adviser during the battle for the presidency, also rejected any idea of misconduct in the ouster of FBI Director James Comey and vowed to defend his honour "against scurrilous and false allegations".
In his dramatic appearance before former colleagues, Sessions contradicted a contention made by Comey at a hearing before the same panel last week.
Comey told the intelligence committee that, after an encounter with President Trump in which he said Trump pressured him to back off an investigation into the former national security adviser, Comey "implored" Sessions to make sure he was never left alone with the president again - but that Sessions didn't respond.
"He didn't recall this, but I responded to his comment by agreeing that the FBI and Department of Justice needed to be careful to follow department policy regarding appropriate contacts with the White House," Sessions said.
The former Alabama senator also defended himself against accusations that he misrepresented himself during his confirmation hearing when he said he hadn't met with Russian officials during the campaign.
Sessions argued that in the context of that hearing, "my answer was a fair and correct response to the charge as I understood it."
The attorney general stepped aside from the Justice Department probe into Russian meddling in the campaign on March 2, the day after The Washington Post reported on two previously undisclosed meetings with Russian Ambassador Sergey Kislyak.
Days after that, Sessions also corrected his confirmation hearing testimony to inform the committee about his two meetings with Kislyak.
Ahead of the hearing there had been suggestions that Sessions might have had a third, unreported, encounter with Kislyak in April 2016, at Washington's Mayflower Hotel, where candidate Trump was giving his first major foreign policy speech.
Sessions was adamant that he did not have a private meeting with Kislyak at that event. He did allow for the possibility that he encountered him in a reception that he said was attended by a couple dozen people, though he said he had no specific recollection of that.