investigation into Russia's interference in last year's presidential election, three U.S. officials said Wednesday.
The officials said Comey met last week with Rod Rosenstein, the deputy attorney general, to make the request. Comey then alerted lawmakers with ties to the concurrent congressional investigations into Russia's meddling, according to the officials, who insisted on anonymity in order to disclose the private conversations.
Justice Department spokeswoman Sarah Isgur Flores said it was false that Comey had asked Rosenstein for money for the Russia investigation.
The revelations raise new questions about what prompted Trump's decision to fire Comey. The White House has cited a memo from Rosenstein, in which he criticizes Comey's handling of last year's investigation into Democrat Hillary Clinton's email practices.
Rosenstein's memo makes no mention of the FBI's Russia investigation, which is probing both Russia's hacking of Democratic groups last year and whether Trump campaign associates had ties to Moscow's election interference.
Trump defended his decision Wednesday, asserting in a flurry of tweets that both Democrats and Republicans "will be thanking me" for his action. He did not mention any effect the dismissal might have on the FBI and congressional investigations into contacts between his 2016 election campaign and Russia.
"He wasn't doing a good job. Very simply. He was not doing a good job," Trump said in brief remarks to reporters in the Oval Office, where he was joined by former Secretary of State Henry Kissinger.
The White House said Trump had been considering firing Comey since the election.
"I think it has been an erosion of confidence," White House spokeswoman Sarah Huckabee Sanders said. She said Rosenstein's memo, as well as Comey's own testimony last week on his handling of the Clinton investigation, pushed Trump toward a final decision.
The abrupt firing of Comey threw into question the future of the FBI's investigation and immediately raised suspicions of an underhanded effort to stymie a probe that has shadowed the administration from the outset. Trump has ridiculed the investigations as "a hoax" and denied any campaign involvement with the Russians.
Sanders said the White House would "encourage" the FBI to complete the Russia investigation. She said the president continued to oppose appointing a special prosecutor to oversee the investigation.
Democrats compared Comey's ouster to President Richard Nixon's "Saturday Night Massacre" during the Watergate investigation and renewed calls for the appointment of a special prosecutor.
Ironically, Kissinger, who was meeting with Trump, was Nixon's secretary of state in 1973, just moved over from being Nixon's national security adviser.
Earlier Wednesday, Senate Democratic leader Chuck Schumer of New York urged Attorney General Jeff Sessions and his deputy, Rosenstein, to appear before the Senate to answer questions about the circumstances surrounding Trump's action.
However, Senate Majority Leader Mitch McConnell brushed aside calls for a special prosecutor, saying a new investigation into Russian meddling would only "impede the current work being done." He noted that Democrats had repeatedly criticized Comey in the past and some had called for his removal.
Trump made a similar case on Twitter, saying Comey had "lost the confidence of almost everyone in Washington," adding: "When things calm down, they will be thanking me!"
Vice President Mike Pence said at the Capitol that Trump had made "the right decision at the right time."
The Justice Department said Sessions was interviewing candidates to serve as an interim replacement. Comey's deputy, FBI veteran Andrew McCabe, became acting director after Comey was fired.
In his brief letter Tuesday to Comey, Trump said the firing was necessary to restore "public trust and confidence" in the FBI. The administration paired the letter with a scathing review by Rosenstein, the recently confirmed deputy attorney general, of how Comey handled the investigation into Clinton's email practices, including his decision to hold a news conference announcing its findings and releasing "derogatory information" about Clinton.
"You can't make this stuff up," Rep. Adam Schiff of California, top Democrat on the House intelligence committee, said Wednesday on MSNBC. As to Trump's contention that the firing had to do with Comey's decision-making on such matters as the Clinton emails, he said, "Nobody believes that."
Trump, in his letter, pointedly thanked Comey for telling him three times "that I am not under investigation." The FBI has not confirmed that Comey ever made those assurances to the president. In public hearings, Comey has declined to answer when asked if Trump is under investigation, urging lawmakers not to read anything into that statement.
While Comey has drawn anger from Democrats since he reopened the email investigation in the closing days of last year's campaign, they didn't buy that justification for his firing. Several Republicans joined them in raising alarms of how it could affect probes into possible coordination between Trump associates and Russia to influence the election.
In one of the strongest statements by Republicans, Sen. Richard Burr of North Carolina, chairman of the Senate intelligence committee, said, "I am troubled by the timing and reasoning of Director Comey's termination."
"His dismissal further confuses an already difficult investigation by the committee," Burr said.
Schumer told Trump in a phone call he thought dumping Comey was a mistake. On Wednesday, Trump labeled the Senate minority leader "Cryin' Chuck Schumer."
Trump will now appoint a successor at the FBI, which has been investigating since late July, and who will almost certainly have an impact on how the probe moves forward and whether the public will accept its outcome.
It was only the second firing of an FBI director in history. President Bill Clinton dismissed William Sessions amid allegations of ethical lapses in 1993.
Republican Sen. John McCain of Arizona said Congress must form a special committee to investigate Russia's interference in the election.
Comey, 56, was nominated by President Barack Obama for the FBI post in 2013 to a 10-year term, though that appointment does not ensure a director will serve the full term.
Praised frequently by both parties for his independence and integrity, he spent three decades in law enforcement. Before the past months' controversies, the former deputy attorney general in the George W. Bush administration was perhaps best known for a remarkable 2004 standoff with top officials over a federal domestic surveillance program. In March of that year, Comey rushed to the hospital bed of Attorney General John Ashcroft to physically stop White House officials in their bid to get his ailing boss to reauthorize a secret no-warrant wiretapping program.
But his prominent role in the 2016 presidential campaign raised questions about his judgment and impartiality. Though the FBI did not recommend charges against Clinton for mishandling classified information, Comey was blisteringly critical of her decision to use a personal email account and private internet server during her four years as secretary of state.
Comey strongly defended his decisions during a Senate Judiciary Committee hearing last week. He said he was "mildly nauseous" at the thought of having swayed the election but also said he would do the same again.
Clinton has partially blamed her loss on Comey's disclosure to Congress less than two weeks before Election Day that the email investigation would be revisited. Comey later said the FBI, again, had found no reason to bring any charges.