Hillary Clinton leads Donald Trump by 15 percentage points among early voters in the US presidential election, according to a new poll.

The Reuters/IPSOS States of the Nation survey, released 11 days before polling day, shows the Democratic nominee is ahead of Republican candidate Mr Trump among people who have already voted in key swing states such as Ohio and Arizona.

Mrs Clinton also holds an early lead in some core Republican strongholds, including Georgia and Texas, although Mr Trump is still forecast to win these states once all votes are counted. The survey does not include early voter data for every state.

Hillary Clinton attacks FBI handling of email review

Around 19 million Americans – up to 20 per cent of the electorate – have already voted in the election, according to the University of Florida’s United States Election Project.

The survey suggests Mrs Clinton is likely to win 47 per cent of the overall vote, compared to 40 per cent for Mr Trump. That would give her 320 electoral college votes – taking her over the threshold of the 270 needed to win the White House. Mr Trump would win 174 votes in the electoral college, the analysis suggests.

The huge lead among early voters will be a boost for the Clinton campaign after it suffered a potential setback on Friday when the FBI announced it was examining newly uncovered emails sent by Huma Abedin, a close adviser to Mrs Clinton.

The emails were discovered during an investigation into whether former congressman Anthony Weiner, who is Ms Abedin’s estranged husband, sent explicit messages to an underage girl.

The Reuters/IPSOS survey was conducted before news of the new FBI investigation broke. While the full impact of the announcement on the balance of the race remains unclear, the poll suggests some states that were previously leaning towards Mrs Clinton were now too close to call.

The Democrat’s lead was reduced in the battleground states of Pennsylvania, Colorado, Iowa and Nevada. Another, Ohio, is also on a knife-edge.

Mrs Clinton, however, is still reported to be ahead in key marginals of Florida and North Carolina.

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The FBI has previously investigated Mrs Clinton for using a private email server when she was US Secretary of State.

It closed its investigation in the summer, determining that no criminal charges should be brought but criticising Mrs Clinton for being "extremely careless".

The timing of the latest FBI announcement was condemned by a Clinton campaign spokesman, who said he was “confident” the candidate would be cleared of wrongdoing.

But with the outcome of the enquiry unlikely to be announced before the 8 November election, the announcement could narrow the race after weeks in which Mrs Clinton appeared to have pulled ahead.

Polls have given the Democrat a lead of between four and seven points over Mr Trump after the Republican was hit by a series of accusations - denied by the candidate - that he had sexually assaulted several women.

Mr Trump has repeatedly claimed the use of private emails shows Mrs Clinton is untrustworthy and seeks to avoid transparency. The latest investigation was “bigger than Watergate”, he said.

He has previously threatened to put his rival in prison if he becomes president, adding that her email use amounted to "criminal action [that] was wilful, deliberate, intentional and purposeful".