Giving Comey the boot ameliorated "great pressure", Trump told Russian officials during a May 10 meeting in the White House, at least according to a version of the events leaked to the New York Times.
Mr Trump has denied any collusion with Russian Federation, and called the investigation into his campaign the "single greatest witch hunt of a politician in American history". "He was insane, a real nut job", MrTrump said, according to the New York Times, which cited a document read to it by a U.S. official.
"This new report that President Trump openly admitted to the Russians that he "faced great pressure" from the FBI's criminal investigation that was "taken off" when he fired Director Comey is astonishing - and extremely troubling", Cummings said.
Capping days of political drama in Washington, Mueller's appointment came as Trump fends off a stunning series of allegations including claims he shared USA secrets with Russian officials in the Oval Office.
The NYT noted that a government official briefed on the meeting said the president was deploying a negotiating tactic "to create a sense of obligation with Russian officials and to coax concessions out of Mr. Lavrov - on Syria, Ukraine and other issues - by saying that Russian meddling in last year's election had created enormous political problems for Mr. Trump". "The investigation would have always continued, and obviously, the termination of Comey would not have ended it". "By grandstanding and politicizing the investigation into Russia's actions, James Comey created unnecessary pressure on our ability to engage and negotiate with Russian Federation".
The Times report on Friday afternoon is just the latest bombshell story over the past week and adds to mounting headaches for the White House just as Trump has departed for his first foreign trip as president.
Trump's dismissal of Comey was met with bipartisan derision. That'd have been way juicier than the ISIS intelligence nugget that blew up into a controversy that barely lasted a day and now feels like ancient history because of the Comey memo story.
After days of turmoil in Washington, the Justice Department announced the appointment on Thursday of a special counsel to look into Russian interference in the 2016 election and possible collusion by the Trump campaign.
A USA official briefed on the conversation said Trump was using "pressure" he faced from Comey as a negotiating ploy to win diplomatic gains from Lavrov on issues of dispute between Washington and Moscow - namely Syria and Ukraine.
Congress members said the third line of investigation was added recently, after memos surfaced claiming Mr Trump had tried to convince his former FBI director to drop an investigation into former national security adviser Mike Flynn.