Several media reports said Mr Comey was addressing staff in the Los Angeles field office when television screens in the background began flashing the news of his fate.
At the same time, Donald Trump’s former bodyguard, Keith Schiller, who now serves as the president’s director of Oval Office operations, delivered by hand a letter to the FBI headquarters in Washington.
The letter informed Mr Comey that he was “hereby terminated and removed from office, effective immediately”, with Mr Trump saying he had reached the conclusion that that he was “not able to effectively lead the bureau”.
“It is essential that we find new leadership for the FBI that restores public trust and confidence in its vital law enforcement mission,” Mr Trump said.
“I wish you the best of luck in your future endeavours.”
ABC News said Mr Comey had been in Los Angeles for a field office inspection and a recruitment event, scheduled for Tuesday evening, that was part of the FBI's efforts to boost diversity.
One FBI official said that Mr Comey was “surprised, really surprised” and was “caught flat-footed”, when he learned the news. It seemed that Mr Comey decided to scrap his speaking engagement in Los Angeles and return to Washington. CNN showed footage of Mr Comey’s vehicle convoy travelling a Los Angeles freeway.
A letter from Attorney General Jeff Sessions to the president was also released by the White House. Mr Sessions - who was forced to recuse himself from the investigation into Mr Trump’s alleged links to Russia - said he had concluded “a fresh start is needed at the leadership of the FBI”.
“It is essential that this Department of Justice clearly reaffirm its commitment to longstanding principles that ensure the integrity and fairness of federal investigations and prosecutions,” it said.
“The Director of the FBI must be someone who follows faithfully the rules and principles of the Department of Justice and who sets the right example for our law enforcement officials and others in the Department.”
While testifying in front of the House Committee on Intelligence on March 20, 2017, Mr Comey took the rare step of confirming the FBI was investigating alleged Russian interference in the US election and “any links between individuals associated with the Trump campaign and the Russian government and whether there was any coordination between the campaign and Russia's efforts”.
The White House also said Mr Comey had erred by revealing that Hillary Clinton’s use of a private email server was being probed.
A letter from Deputy Attorney General Rod Rosenstein credited Mr Comey with being “an articulate and persuasive public speaker about leadership” but goes on to note that he “cannot defend the Director's handling of the conclusion of the investigation of Secretary Clinton's emails, and I do not understand his refusal to accept the nearly universal judgment that he was mistaken”.
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