The FBI has obtained a warrant to search the emails of US presidential candidate Hillary Clinton discovered last week, providing a boost to Donald Trump's campaign less than two weeks before the election.
Some 650,000 emails exchanged by Clinton and her close confidante Huma Abedin are now being searched and the investigation could continue past election day on 8 November.
A federal law enforcement official confirmed the "process has begun", according to The Telegraph.
The emails were discovered as part of an unrelated inquiry into New York congressman Anthony Weiner, who is the subject of an underage sexting investigation.
The FBI believes they could be "pertinent" to its previous inquiry into Clinton's use of a private server while Secretary of State, which closed in July without any charges being brought against her.
The latest scandal has provided a boost to Donald Trump's campaign, who has since been targeting Democratic states in an effort to gain last-minute supporters as the gap between the two candidates narrows.
A poll from ABC News/Washington Post on 30 October put Clinton just one point ahead of Trump, compared to a 12-point lead earlier in the week.
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However, FBI director James Comey has been criticised for bringing the new investigation to light so close to the election.
He has been warned by Democratic leader of the US Senate Harry Reid that he could be breaking federal law, which forbids FBI officials from using their authority to influence the election result.
In a letter to Mr Comey, Reid said: "Your actions in recent months have demonstrated a disturbing double standard for the treatment of sensitive information, with what appears to be a clear intent to aid one political party over another.
"I am writing to inform you that my office has determined that these actions may violate the Hatch Act, which bars FBI officials from using their official authority to influence an election. Through your partisan actions, you may have broken the law."
