The Democratic candidate called on the FBI to disclose full details of its investigation
Hillary Clinton and her campaign team have called on the FBI to release all information about the latest development in the investigation into the Democratic candidate's email use.
In a letter made public on Friday, FBI director James Comey revealed the bureau would examine whether newly discovered emails contained sensitive government information.
Mr Comey has faced criticism from Democrats over the handling of the news, while his actions have been warmly welcomed by Republican candidate Donald Trump.
The New York Times reports Mr Comey was 'strongly discouraged' from sending the letter by officials in the US Department of Justice as the move broke with previous policy.
The New Yorker suggests that he also was acting independently of US Attorney General Loretta Lynch.
Matthew Miller, a former chief spokesman for the US Department of Justice, told Sky News: "There are rules in place that really are supposed to limit how the FBI handles these types of situations and they are not supposed to make these types of public statements so close to an election, especially when there is no evidence at all that we know of that anyone did anything wrong."
Clinton campaign chair John Podesta said: “It is extraordinary that we would see something like this just 11 days out from a presidential election."
The FBI had concluded in July that Mrs Clinton was "extremely careless" in handling classified information while Secretary of State, with scores of emails on her private server containing highly classified information.
But the bureau did not recommend criminal charges.
Responding at a hastily arranged news conference, Mrs Clinton demanded the FBI disclose full details of its new probe, which came to light just 11 days before the election.
"The American people deserve to get the full and complete facts immediately," Mrs Clinton told reporters in Iowa.
"It's imperative that the bureau explains this issue in question, whatever it is, without any delay."
The messages were discovered after the FBI seized four electronic devices belonging to Mrs Clinton's aide Huma Abedin and her husband Anthony Weiner, the New York Times reported.
They were taken during an investigation into illicit text messages between the former Congressman and a 15-year-old girl.
An unnamed US official told Associated Press the new emails did not come from Mrs Clinton's private server.
The news prompted a hasty response from Mrs Clinton's Republican rival Donald Trump, who told his supporters the development is "bigger than Watergate".
At a rally in New Hampshire, Mr Trump said: "Hillary Clinton's corruption is on a scale we have never seen. We must not let her take her criminal scheme into the Oval Office."