WASHINGTON - President Donald Trump asked then-FBI Director James Comey to end the agency's investigation into ties between former White House national security adviser Michael Flynn and Russia, according to a source who has seen a memo written by Comey.

The explosive new development on Tuesday followed a week of tumult at the White House after Trump fired Comey and then discussed sensitive national security information about Islamic State with Russian Foreign Minister Sergei Lavrov.

The Comey memo, first reported by the New York Times, is likely to raise questions about whether Trump tried to interfere with a federal investigation.

The White House quickly denied the report, saying in a statement it was "not a truthful or accurate portrayal of the conversation between the president and Mr. Comey."

Comey wrote the memo after he met in the Oval Office with Trump, the day after the Republican president fired Flynn on Feb. 14 for misleading Vice President Mike Pence about the extent of his conversations last year with Russia's ambassador, Sergei Kislyak.

“I hope you can let this go,” Trump told Comey, according to a source familiar with the contents of the memo.

The New York Times said that during the Oval Office meeting, Trump condemned a series of government leaks to the news media and said the FBI director should consider prosecuting reporters for publishing classified information.

Coming the day after charges that Trump disclosed sensitive information to the Russians last week, the new disclosure further rattled members of Congress.

"The memo is powerful evidence of obstruction of justice and certainly merits immediate and prompt investigation by an independent special prosecutor," said Democratic U.S. Senator Richard Blumenthal.

Republican and Democratic lawmakers said they wanted to see the memo.

Republican Rep. Jason Chaffetz, chairman of a House of Representatives oversight committee, said his committee "is going to get the Comey memo, if it exists. I need to see it sooner rather than later. I have my subpoena pen ready."

In a letter to acting FBI Director Andrew McCabe, Chaffetz set a deadline of May 24 for the FBI to produce "all memoranda, notes, summaries, and recordings referring or relating to any communications between Comey and the President."

Republican Speaker of the House Paul Ryan backed Chaffetz.

"We need to have all the facts, and it is appropriate for the House Oversight Committee to request this memo," said Ryan spokeswoman AshLee Strong.

LEGAL QUESTIONS

Legal experts took a dim view of Trump's comments, as quoted in the memo.

"For the president to tell the FBI to end a potential criminal investigation, that's obstruction of justice," said Erwin Chereminsky, a constitutional law professor and dean of University of California, Irvine School of Law. "This is what caused President Nixon to resign from office."

But the experts said intent was a critical element of an obstruction of justice charge, and the president’s words could be subject to interpretation and possibly put into the context of other actions, like Comey’s termination.

The fact that the president apparently said he “hoped” Comey would end the Flynn investigation rather than more directly ordering it “makes for a weaker but still viable case,” said Christopher Slobogin, a criminal law professor at Vanderbilt University Law School.

Flynn's resignation came hours after it was reported that the Justice Department had warned the White House weeks earlier that Flynn could be vulnerable to blackmail for contacts with Kislyak before Trump took office on Jan. 20.

Kislyak was with Lavrov at the White House when Trump disclosed the sensitive information.

A spokeswoman for the FBI declined to comment on the details of the memo.

An emailed fundraising appeal by Trump's political organization and the Republican National Committee sent out after reports of the Comey memo said Trump was being victimized by an "unelected bureaucracy."

"You already knew the media was out to get us," it said. "But sadly it’s not just the fake news… There are people within our own unelected bureaucracy that want to sabotage President Trump and our entire 'America First' movement."

The new development came as Republican and Democratic lawmakers pressured Trump to give a fuller explanation for why he revealed sensitive intelligence information to Lavrov.

The information had been supplied by a U.S. ally in the fight against the Islamic State militant group, the officials said.

REACTIONS FROM CAPITOL HILL

"@GOPoversight is going to get the Comey memo, if it exists. I need to see it sooner rather than later. I have my subpoena pen ready." – Republican Representative Jason Chaffetz, chairman of the House Oversight and Government Reform Committee, on Twitter

"This is an explosive allegation and it appears like a textbook case of criminal obstruction of justice. We need to hear testimony immediately from Director Comey - in public ... We also obviously need to get Director Comey’s memos immediately, as well as all associated records, including any audio tapes, and notes, if they exist." – Democratic Representative Elijah Cummings in a statement

"I don't want to read a memo. I want to hear it from him (Comey)." – Republican Senator Lindsey Graham in an MSNBC interview

"The memo is powerful evidence of obstruction of justice and certainly merits immediate and prompt investigation by an independent special prosecutor. If there were ever a final nail on the case for an independent, special prosecutor this is it." – Democratic Senator Richard Blumenthal to reporters

"I have to say yes simply because obstruction of justice is such a serious offense. And I say it with sadness and reluctance." – Independent Senator Angus King, asked on CNN if Congress was getting close to impeachment proceedings

"We're a long ways from a conviction – the fact that we simply have a headline in the New York Times." – Republican Representative Trey Gowdy on Fox News

"If true, this is yet another disturbing allegation that the president may have engaged in some interference or obstruction of the investigation. I think we know enough now. There's been enough alleged publicly to want to bring the director back to testify, ideally in open session, either before our committee or the Judiciary Committee." – Democratic Representative Adam Schiff to reporters

"Country must have answers. It is clear former FBI Director Comey should testify before Congress." – Republican Representative Frank LoBiondo on Twitter

"If these reports are true, the president's brazen attempt to shut down the FBI's investigation of Michael Flynn is an assault on the rule of law that is fundamental to our democracy. At best, President Trump has committed a grave abuse of executive power. At worst, he has obstructed justice." – Democratic Representative Nancy Pelosi in a statement

"I’m shocked and surprised by this development and would like to discuss it with Chairman Grassley and look forward to doing so. The Judiciary Committee is the appropriate place to hold a hearing and get to the bottom of exactly what was said and by whom.” – Democratic Senator Dianne Feinstein in a statement

"The stories of the last week raise serious questions about whether the president respects the independence of the FBI and law enforcement authorities. It is vital that Congress obtain these memos and hear public testimony from former Director Comey ... The American people deserve answers about President Trump’s conduct.” – Democratic Senator Bob Casey in a statement