US President Donald Trump has fired FBI director James Comey, the White House says.
The move was made on the recommendation of Attorney General Jeff Sessions.
"Today, President Donald J Trump informed FBI Director James Comey that he has been terminated and removed from office," a White House statement said.
In a letter obtained by The Washington Post, Mr Trump tells Mr Comey that while he appreciates being told that he was not under investigation, "I nevertheless concur with the judgment of the Department of Justice that you are 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 Comey had been leading an inquiry into alleged links between the Trump election campaign and Russia.
The White House said the search for a successor would begin immediately.
The surprise move comes after Mr Comey acknowledged giving inaccurate information about Hillary Clinton's emails to Congress last week.
Mrs Clinton has blamed Mr Comey for her election defeat to Mr Trump.
The FBI director made two interventions during the election campaign - first in July and again in October - to make pronouncements about an FBI investigation into Mrs Clinton's private email server.
Mr Comey told lawmakers last week that Mrs Clinton's top aide, Huma Abedin, had forwarded "hundreds and thousands" of classified emails to her then-husband.
But investigating officials conceded on Tuesday that the emails were only a handful in number and most were not classified.
Appearing in front of the Senate Judiciary Committee on 3 May, Mr Comey said: "Huma Abedin appears to have had a regular practice of forwarding emails to him [then-husband Anthony Weiner] for him I think to print out for her so she could then deliver them to the secretary of state."
But the agency's assistant director of Congressional Affairs, Gregory Brower, said in a letter to the congressional committee on Tuesday that Ms Abedin only sent two email chains containing classified information to her husband for printing.
The majority of the 49,000 emails investigators uncovered on her husband's computer were transferred via backup of her work Blackberry device, Mr Brower wrote.
A further 10 email chains containing classified information were discovered on Mr Weiner's computer as a result of this backup.
Ultimately, all 12 classified email chains were determined to have been previously reviewed by investigators who came across them via other electronic devices.