Justice Department was told to come up with reasons to fire Comey, reports say

The Department of Justice was told to come up with justification to fire FBI Director James Comey, The New York Times and CNN reported Tuesday.

White House and Justice Department officials "had been working on building a case against [Comey] since at least last week," according to the Times, which cited administration officials. The report said Attorney General Jeff Sessions "had been charged with coming up with reasons to fire him."

President Donald Trump fired Comey on Tuesday, telling him in a letter "it is essential that we find new leadership for the FBI that restores public trust and confidence in its vital law enforcement mission." In letters released publicly, Sessions and Deputy Attorney General Rod Rosenstein recommended that Comey be fired due to his conduct in the investigation into Hillary Clinton's handling of classified information at the State department.

Several lawmakers questioned the timing of Comey's removal because the FBI is investigating Russia's alleged interference in the 2016 presidential election, including any possible links between the Trump campaign and Moscow.

White House spokesman Sean Spicer said Trump had only received the memo from Rosenstein on Tuesday and decided to fire Comey based on it.

The White House did not immediately respond to CNBC's request to comment on this story, but Trump advisor Kellyanne Conway claimed to CNN on Tuesday that the firing "is not a cover up" and had "nothing" to do with Russia.

Three senior FBI and Department of Justice officials told NBC News that they had no warning or advance knowledge of Comey's dimissal. Some of the officials that spoke with NBC know Comey personally.

Democratic Sen. Chuck Schumer responded to Comey's dismissal by calling for a special prosecutor in the investigation of ties between Donald Trump's campaign and Russia.

"I have said from the get-go that I think a special prosecutor is the way to go, but now with what's happened it is the only way to go," Schumer told reporters on Tuesday.

The White House said its search for Comey's successor begins immediately.

—CNBC's Christine Wang contributed to this report.