US President Donald Trump has fired the director of the FBI over his handling of the inquiry into Hillary Clinton's emails, the administration says.
The White House shocked Washington by announcing that James Comey "has been terminated and removed from office".
But Democrats said he was fired because the FBI was investigating alleged links between the Trump campaign and Russia.
The move came as it emerged Mr Comey gave inaccurate information about Mrs Clinton's emails to Congress last week.
Mr Comey was addressing FBI agents in Los Angeles when, according to Politico and the New York Times, he learned he had just been fired when he saw the news on television.
The 56-year-old - who was three and a half years into his 10-year term as FBI director - reportedly laughed, thinking it was a prank.
The White House said the search for a successor would begin immediately. It is only the second time for the head of the FBI to be fired.
Why does the administration say Comey was fired?
President Trump wrote in a letter to Mr Comey that he agreed with US Attorney General Jeff Sessions' recommendation that "you are not able to effectively lead the Bureau".
Mr Sessions said the Department of Justice was "committed to a high level of discipline, integrity, and the rule of law", and "a fresh start is needed".
Many have expressed surprise that Mr Comey should be fired for his handling of the investigation into Mrs Clinton's use of a private email server for sensitive government business, given that Mr Trump once praised the FBI director's conduct in the matter.
In the final days of the presidential campaign, Mr Trump told a rally it "took guts" for Mr Comey to reopen the inquiry. "What he did brought back his reputation," Mr Trump said.
But on Tuesday, Deputy Attorney General Rod Rosenstein said he "cannot defend the director's handling of the conclusion of the
"Almost everyone agrees the director made serious mistakes; it is one of the few issues that unites people of diverse perspectives."
What about the Russia investigation?
Democrats swiftly suggested that Mr Trump had fired Mr Comey to influence the FBI inquiry into whether members of the Trump election campaign colluded with the Kremlin.
The House of Representatives and Senate intelligence committees are looking into the same allegations.
"Were these investigations getting too close to home for the president?" Senate Minority Leader Chuck Schumer asked a Tuesday evening press conference.
"This does not seem to be a coincidence," he added.
Mr Trump responded on Twitter that Mr Schumer had recently expressed his lack of confidence in the FBI chief.
The firing is drawing comparisons with the so-called Saturday Night Massacre of 1973, when President Richard Nixon fired an independent special prosecutor investigating the Watergate scandal.
But President Trump has repeatedly insisted the Russia allegations are "fake news".
A cover-up? Anthony Zurcher, BBC News, Washington
Donald Trump and senior Justice Department officials are framing the firing of James Comey as a result of his botched investigation into Hillary Clinton's email server. They do so using language that even Clinton backers would probably support.
Democrats, to put it bluntly, aren't buying it, however - not from this White House. They are dismissing this Clinton explanation as a smokescreen, and view the suddenness of the move as an attempt to subvert the ongoing FBI investigation into possible ties between Russia and the Trump campaign.
At the very least, their calls for an independent investigation into the matter will become deafening - and some Republicans may now be inclined to agree.