With the Republican president facing a storm of criticism from many Democratic lawmakers and some in his own party, the Trump administration accused Comey of "atrocities" on the job and denied his firing was related to the FBI's Russia investigation, Reuters reports.
Trump, who met Russia's foreign minister at the White House on Wednesday, lashed out at critics, calling Democrats "phony hypocrites," and defended his decision to abruptly oust Comey on Tuesday from the law enforcement post he held since 2013.
In a farewell letter to staff seen by CNN, Comey, who was appointed by Trump's predecessor, Democratic President Barack Obama, said he had "long believed that a president can fire an FBI director for any reason, or for no reason at all."
Read alsoCNN: Trump fires FBI director James ComeyA congressional source with knowledge of the matter said Comey told lawmakers within the past few days he had asked the Justice Department to make additional resources available - mainly more staffing - for the Russia probe.
Comey informed lawmakers of that request after the Senate Intelligence Committee, conducting its own investigation, had asked the FBI to speed up its Russia inquiry, the source said.
Democrat Dianne Feinstein, the Senate Judiciary Committee's top Democrat, told reporters she understood Comey was seeking more resources for the FBI investigation.
Read alsoSen. McCain "disappointed" over Comey dismissalComey's dismissal stunned Washington and plunged Trump deeper into a controversy over his campaign's alleged ties with Russia that has dogged the early days of his presidency, while also threatening to hinder his policy goals.
The administration said on Tuesday that Comey's firing stemmed from his handling of an election-year FBI probe into Democratic presidential nominee Hillary Clinton's use of a private email server during her time as secretary of state.