WASHINGTON (REUTERS) - Federal investigators have secured a warrant to examine newly discovered e-mails related to Mrs Hillary Clinton's private server, US media reported, as a prominent Democrat accused FBI director James Comey of breaking the law by trying to influence the election.

The warrant will allow the Federal Bureau of Investigation (FBI) to examine the e-mails to see if they are relevant to its probe of the private e-mail server used for government work by Mrs Clinton, the Democratic presidential nominee, while she was secretary of state from 2009 to 2013.

FBI officials were unavailable for comment on the status of their investigation. Reuters could not independently confirm that the search warrant had been issued.

Mr Comey came under heavy pressure from Democrats on Sunday (Oct 30) to quickly provide details of the e-mails, as Clinton allies worried that the prolonged controversy could extend beyond the Nov 8 election and cast a shadow over a Clinton transition if she wins the White House.

Mr Comey's disclosure of the e-mail discovery in a letter to Congress on Friday plunged the final days of the White House race between Mrs Clinton and Republican Donald Trump into turmoil. Mrs Clinton had opened a recent lead over Mr Trump in national polls, but it had been narrowing even before the e-mail controversy resurfaced.

US Senate Democratic leader Harry Reid sent a letter to Mr Comey on Sunday suggesting he had violated the Hatch Act, which bars the use of a federal government position to influence an election.

"Through your partisan actions, you may have broken the law," Mr Reid, a senator from Nevada, said in the letter to Mr Comey.

Clinton campaign chairman John Podesta and campaign manager Robby Mook questioned Mr Comey's decision to send a letter notifying Congress of the e-mail review before he even knew whether they were significant or relevant.

Mr Comey's letter was "long on innuendo, short on facts", Mr Podesta said on CNN's State of the Union programme, and accused the FBI chief of breaking precedent by disclosing aspects of an investigation so close to the election.

"We are calling on Mr Comey to come forward and explain what's at issue here," he said, adding the significance of the e-mails was unclear.

"He might have taken the first step of actually having looked at them before he did this in the middle of a presidential campaign, so close to the voting," he added.

Mr Comey's letter was sent over the objections of Justice Department officials. But those officials did not try to stop the FBI from getting the warrant, a source familiar with the decision said, because they are interested in the FBI moving quickly on the probe.

Sources close to the investigation have said the latest e-mails were discovered as part of a separate probe of former Democratic US Representative Anthony Weiner, the estranged husband of Clinton aide Huma Abedin.

Mr Weiner is the target of an FBI investigation into illicit text messages he is alleged to have sent to a 15-year-old girl in North Carolina. The FBI already had a warrant to search his laptop in that probe, but needed a warrant to look at the material that might be related to Mrs Clinton.

'CHECK ON CORRUPTION'

Sources familiar with the matter said FBI agents working on the Weiner investigation saw material on a laptop belonging to Mr Weiner that led them to believe it might be relevant to the investigation of Mrs Clinton's e-mail practices.

Mr Trump has highlighted the issue as proof for his argument that Mrs Clinton is corrupt and untrustworthy.

"We have one ultimate check on Hillary's corruption and that is the power of the vote," Mr Trump told a rally in Las Vegas on Sunday. "The only way to beat the corruption is to show up and vote by the tens of millions."

Mr Comey, who announced in July that the FBI's long investigation of Mrs Clinton's e-mails was ending without any charges, said in his letter the agency would review the newly surfaced e-mails to determine their relevance to the investigation of her handling of classified information.

Prof Richard Painter, a professor at the University of Minnesota Law School and the chief White House ethics lawyer from 2005 to 2007, said he filed a complaint over Mr Comey's actions with the Office of Special Counsel, which investigates Hatch Act violations.

"We cannot allow FBI or Justice Department officials to unnecessarily publicise pending investigations concerning candidates of either party while an election is underway. That is an abuse of power," he said in a column in the New York Times.

But Mr Daniel Richman, a former federal prosecutor who now teaches at Columbia Law School, called the allegations that Mr Comey improperly tried to influence the election "inane".

"Comey's critics cannot show his letter violated the Hatch Act unless they can prove that the FBI director was intending to influence the election rather than inform Congress, which was Comey's stated aim," said Mr Richman, who said he had advised Mr Comey on law enforcement policy but not this issue.

An ABC News/Washington Post poll released on Sunday showed Mrs Clinton with a statistically insignificant one-point national lead on Mr Trump. About a third of likely voters in the poll said they were less likely to back Mrs Clinton given the disclosure.

Mrs Clinton, who told a Florida rally on Saturday that Mr Comey's letter was "deeply troubling", did not address the issue directly on Sunday but referred vaguely to voters overcoming a"distraction".

"There's a lot of noise and distraction but it really comes down to the kind of future we want and who can get us there," she told a packed gay nightclub in Wilton Manors, Florida, where hundreds of supporters who could not get in lined the streets outside.

"We don't want a president who would appoint Supreme Court justices to overturn marriage equality," she said.