New emails the FBI is examining related to Democratic presidential candidate Hillary Clinton's use of a private computer server were discovered after the agency seized electronic devices belonging to Clinton aide Huma Abedin and her husband, Anthony Weiner, the New York Times reports, citing law enforcement officials.
But Ms Clinton said she did not believe it would impact its conclusion made back in July.
She added that the American people deserved to get the full and complete facts from the probe.
With just 11 days to go before the November 8 election, FBI Director James Comey said in a letter to several congressional Republicans on Friday that the agency had learned of the existence of emails that appeared to be pertinent to its investigation.
However, he said the FBI did not know if the emails were significant and did not provide a time frame for the probe.
Clinton campaign chairman John Podesta said the FBI should immediately provide more information about the latest email discovery.
Republican presidential candidate Donald Trump welcomed the news.
"I have great respect for the fact that the FBI and the Department of Justice are now willing to have the courage to right the horrible mistake that they made," Trump told a campaign rally.
Trump's campaign reacted with glee. His campaign manager, Kellyanne Conway, said on Twitter that "a great day in our campaign just got even better".
US House of Representatives Speaker Paul Ryan renewed his call for US intelligence officials to stop giving Clinton classified briefing typically given to presidential candidates in the wake of the probe.
"This decision, long overdue, is the result of her reckless use of a private email server, and her refusal to be forthcoming with federal investigators. I renew my call for the Director of National Intelligence to suspend all classified briefings for Secretary Clinton until this matter is fully resolved," Ryan said in a statement referring to the former secretary of state.
The resurrection of the email issue, which has dogged Clinton's campaign from the start, dimmed a day that had featured good news for her effort to win the White House.
The Commerce Department reported that the economy grew at a 2.9 per cent annual rate in the third quarter, its fastest pace in two years and higher than the expected 2.6 per cent, thanks to a surge in exports and a rebound in investment.
The report had bolstered Clinton, who has positioned herself as the best candidate to continue years of economic expansion under Democratic President Barack Obama.
More Americans say jobs and the economy are their No. 1 priority when they decide who to vote for than any other issue.
Trump argues that as a successful businessman and political outsider, he is the best person to take a new approach to rebuilding an economy that has sent too many jobs overseas and left many Americans struggling to find decent jobs.
Clinton's camp said Friday's report showed "real progress" since Obama took office in 2009, when the country was struggling to emerge from economic recession.
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The chairman of Hillary Clinton's presidential campaign said on Friday that the campaign was "confident" the FBI would again recommend against pressing charges against the former secretary of state relating to her use of a private email server once it wraps up the latest leg of its investigation.
"The (FBI) Director owes it to the American people to immediately provide the full details of what he is now examining," campaign chairman John Podesta said in a statement after the FBI said it was examining new emails for whether they contained classified information.
"We are confident this will not produce any conclusions different from the one the FBI reached in July," he said.
The White House on Friday said it was not given any prior notice on the FBI's announcement that it was investigating additional emails relating to Hillary Clinton's use of a private email system.
"We did not have advance warning," White House spokesman Eric Schultz told reporters traveling with President Barack Obama to a campaign event for Clinton in Orlando, Florida.
Schultz said news of the Federal Bureau of Investigation probe has not affected Obama's support for Clinton. "I don't think anything has surfaced to changed the president's opinion and views of Secretary Clinton," he said.
