Hillary Clinton called on the FBI on Friday to release more information about its review of emails that may be related to its investigation into her private server.

"It's imperative that the bureau explain this issue in question, whatever it is, without any delay," she said, adding that she was confident whatever the emails are "will not change the conclusion reached in July."

The Democratic presidential candidate said the American people deserve to have as much information as possible before they vote on Nov. 8. Asked if she feared the news would put a dent in support for her at the polls, Clinton said, "I think people made up their minds about the emails a long time ago."

She spoke Friday evening following a campaign rally in Iowa, hours after the FBI told Congress it is investigating whether new emails that may contain classified information have emerged in its probe of Hillary Clinton's private server, an unexpected announcement that surfaced less than two weeks before the presidential election.

In a letter sent to congressional leaders, FBI Director James Comey said that new emails have come to light recently that have prompted investigators to take another look at the sensitive government information that flowed through the private email sever Clinton used while serving as secretary of state.

"In connection with an unrelated case, the FBI has learned of the existence of emails that appear to be pertinent to the investigation," Comey wrote. "I agreed that the FBI should take appropriate investigative steps designed to allow investigators to review these emails to determine whether they contain classified information, as well as to assess their importance to our investigation."

Comey stressed in his letter that the FBI could not yet assess "whether or not this material may be significant," or how long it might take to run down the new investigative leads.

There is no indication, according to a senior law enforcement official, that Clinton, her campaign or the State Department was withholding information.

The official told NBC News that Comey's letter was sent to the Hill "out of an abundance of caution" and to be extra-thorough, noting there it was unknown what the significance of these letters is.

It was not clear from Comey's letter where the new emails came from or who sent or received them. Sources told NBC News the emails came from electronic devices belonging to Clinton aide Huma Abedin in a separate sexting probe of her husband former congressman Anthony Weiner.

Clinton called the reports "rumors" and told reports Friday she couldn't confirm whether the emails came from devices belonging to Abedin or Weiner.

"That's why it is incumbent upon the FBI to tell us what they're talking about. Because right now your guess is as good as mine, and I don't think that's good enough," she said.

Clinton's campaign manager John Podesta called for Comey to "immediately" release the full details of new emails, and blasted Trump and Republicans for pressing the FBI to revisit their decision to not charge Clinton "in a desperate attempt to harm [her] presidential campaign."

"FBI Director Comey should immediately provide the American public more information than is contained in the letter he sent to eight Republican committee chairmen. Already, we have seen characterizations that the FBI is 'reopening' an investigation but Comey's words do not match that characterization," Podesta said in a statement.

He added: "It is extraordinary that we would see something like this just 11 days out from a presidential election."

Asked to respond to the news from Comey and what it’s about, a top Clinton campaign spokesperson told NBC News, “No idea.”

Democratic vice presidential nominee Tim Kaine said earlier Friday that he's "got to read a little more" when asked by a reporter about the news while stopping by an early voting site in Tallahassee.

State Department spokesman Mark Toner said the department learned about the FBI letter from news reports and did not get any notification from the FBI. Toner pledged the department would "cooperate to the full extent that we can."

The White House, through a spokesman, also declined to immediately comment.

Speaking at a rally in New Hampshire, Donald Trump praised the FBI's announcement and said Clinton's "illegal conduct" threatens the security of the U.S.

"Hillary Clinton's corruption is on a scale we've never seen before," Trump said. "We must not let her take her criminal scheme into the Oval Office."

The crowed cheered and erupted in chants of "Lock her up!"

Trump added that he has "great respect for the fact that the FBI and the DOJ are now willing to have the courage to right the horrible mistake that they made. This was a grave miscarriage of justice that the American people fully understand. It is everybody’s hope that it is about to be corrected."

Trump's campaign manager Kellyanne Conway tweeted earlier: "A great day in our campaign just got even better. FBI reviewing new emails in Clinton probe."

House Speaker Paul Ryan (R-WI) issued a statement on the FBI's announcement, saying “Yet again, Hillary Clinton has nobody but herself to blame.

"She was entrusted with some of our nation’s most important secrets, and she betrayed that trust by carelessly mishandling highly classified information. 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.”

Rep. Bob Goodlatte, R-Va., the chairman of the House Judiciary Committee, said the FBI's decision reinforces the committee's view that the more that is learned about the server, "the clearer it becomes that she and her associates committed wrongdoing and jeopardized national security."

A yearlong investigation by the FBI focused on whether Clinton sent or received classified information using the private server located in the basement of her New York home, which was not authorized to handle such messages.

Comey said in July that his agents didn't find evidence to support any criminal charges or direct evidence that Clinton's private server was hacked. He suggested that hackers working for a foreign government may have been so sophisticated they wouldn't have left behind any evidence of a break-in.