The FBI has stuck to its conclusion that no charges were warranted in the case of Hillary Clinton's use of a private email server, after a recent review of newly-discovered emails.
FBI director James Comey and US presidential candidate Hillary Clinton. Photo: AFP
FBI director James Comey told Congress on Sunday that the agency had "not changed our conclusions that we expressed in July" about the Democrat presidential candidate's use of the server during her time as secretary of state.
In a letter to Congress, Mr Comey said the agency had completed its review of the new emails and "we have not changed our conclusions that we expressed in July with respect to Secretary Clinton".
"The FBI investigative team has been working around the clock to process and review a large volume of emails from a device obtained in connection with an unrelated criminal investigation," Mr Comey said in the letter.
"During that process, we reviewed all of the communications that were to or from Hillary Clinton while she was secretary of state.
"I am very grateful to the professionals at the FBI for doing an extraordinary amount of high-quality work in a short period of time," Mr Comey said.
Brian Fallon, Mrs Clinton's press secretary, tweeted that her team had been "confident that nothing would cause the July decision to be revisited".
Republican presidential candidate Donald Trump, who just hours ago praised the FBI agents investigating Mrs Clinton as "great", now says the Democrat was protected by a "rigged system".
Donald Trump says Hillary Clinton is being protected by a "rigged system". Photo: AFP
At a rally in Minneapolis after news of the FBI conclusion broke, Mr Trump delivered his standard lines about Mrs Clinton without mentioning the latest news.
"Hillary Clinton will be under investigation for a long long time," he said, before his comments were overtaken by a chant of "Lock her up!"
Newt Gingrich, an adviser to the Republican nominee, tweeted: "Comey must be under enormous political pressure to cave like this and announce something he cant [sic] possibly know."
Republican National Committee Chairman Reince Preibus said that while the probe had not led to criminal charges, it produced evidence that Clinton broke the law and "repeatedly lied to the American people about her reckless conduct."
Mr Comey's letter to Congress, informing it of the newly discovered emails, had thrown Mrs Clinton's presidential race into turmoil.
The FBI director has been heavily criticised by leading Democrats, who allege that the timing of his announcement threatened to influence this week's general election.
The FBI had been investigating whether anyone in Mrs Clinton's operation broke the law as result of a personal email server kept in her Chappaqua, New York, home while she was secretary of state from 2009 to 2013.
The FBI has already established that Mrs Clinton had classified information on a private email server. Mr Comey said in July that the White House hopeful's handling of sensitive material during her 2009-13 tenure as secretary of state was "extremely careless", but cleared her of criminal wrongdoing.
The latest emails came to light during a separate inquiry into top Clinton aide Huma Abedin's estranged husband, former congressman Anthony Weiner.
Devices belonging to Ms Abedin and Mr Weiner were seized in an investigation into whether he sent sexually explicit emails to a 15-year-old girl in North Carolina.
Sunday's campaign stops take Mrs Clinton to Ohio, Michigan, Pennsylvania and New Hampshire, while Mr Trump travels to Iowa, Minnesota, Michigan, Pennsylvania and Virginia.