Only half of Republican voters would accept Hillary Clinton as US president.

If the Democratic nominee wins the election on 8 November, nearly 70 per cent said they believed it would be because of illegal voting or vote rigging, according to a Reuters/Ipsos poll.

Meanwhile, 7 out of 10 Democrats said they would accept a Donald Trump victory and less than 50 per cent would attribute it to illegal voting or vote rigging, the survey found.

The beliefs of Democrat and Republican voters largely reflected the views of their respective nominee.

Mr Trump has repeatedly claimed the presidential election is rigged, despite providing no evidence to support this claim.

He has refused to confirm whether or not he would accept a Clinton victory, saying “I will keep you in suspense” when asked.

Recently, he told a rally in Delaware, Ohio: “I would like to promise and pledge to all of my voters and supporters, and to all of the people of the United States, that I will totally accept the results of this great and historic presidential election — if I win."

He has accused the media, the Justice Department, the Federal Bureau of Investigation and a “global power structure” of conspiring to rig the election against him.

He has also claimed there are “millions of people that are registered to vote that shouldn’t be registered to vote."

Meanwhile Ms Clinton has said she will accept the results of the election, no matter what the outcome.

Reuters said: "The poll showed there is broad concern across the political spectrum about voting issues such as ineligible voters casting ballots, voter suppression, and the actual vote count, but Republicans feel that concern more acutely."

For example, nearly eight out of 10 Republicans are concerned about the accuracy of the final vote count. And though generally they believe they will be able to cast their ballot, only six out of 10 are confident their vote will be counted accurately.

Among Democrats, about six out of 10 are concerned about the vote count. They, too, believe they will be able to cast their ballot, but eight out of 10 are confident their vote will be counted accurately.

Lonna Atkeson, a professor at the University of New Mexico and head of the Center for the Study of Voting, Elections, and Democracy said there was a trend across different categories in the survey results.

"Republicans are just more worried about everything than Democrats," she told Reuters.

Seven out of 10 Republicans also told researchers they are concerned about issues such as vote buying, faulty voting machines, or confusing ballot designs. Six out of 10 Democrats feel the same way.

Nearly eight out of 10 Republicans are concerned that ineligible voters, including non-citizens, will illegally cast ballots. Four out of 10 Democrats feel the same way.

Six out of 10 respondents, regardless of party, say they are concerned about issues such as voter intimidation and suppression.

Atkeson said the level of concern and mistrust in the system, especially among Republicans, is unprecedented.

“I’ve never seen an election like this. Not in my lifetime. Certainly not in modern history.”

The difference, she told Reuters, is Trump. “It has to be the candidate effect.”

She said she was worried the lack of trust could become dangerous. It is one thing to not trust government, but quite another to doubt the election process. “Then the entire premise of democracy comes into question,” she said.

About one in five Democrats said they would protest if their candidate loses. Slightly fewer Republicans said they would do the same. Fewer than one in 10 Democrats said they are prepared to take up arms in opposition compared to fewer than one in 20 Republicans.

Democrats are also are three times as likely to say they would leave the country.

US election 2016: the race for the White House in pictures Show all 12 1 /12 US election 2016: the race for the White House in pictures US election 2016: the race for the White House in pictures Republican U.S. presidential nominee Donald Trump shakes hands with Democratic U.S. presidential nominee Hillary Clinton at the conclusion of their first presidential debate at Hofstra University in Hempstead, New York Reuters US election 2016: the race for the White House in pictures President Barack Obama embraces Democratic nominee Hillary Clinton on stage at the party's convention in Philadelphia US election 2016: the race for the White House in pictures Donald Trump's wife Melania delivered a speech at the GOP convention in Cleveland that was later found to have been cribbed in part from Michelle Obama's 2008 convention address AP US election 2016: the race for the White House in pictures Hillary Clinton talks to reporters aboard her new campaign plane on Labour Day, 5 September, her first 'press conference' since 2015 (Getty Images) US election 2016: the race for the White House in pictures Donald Trump held a joint press conference with Mexican leader Enrique Pena Nieto in Mexico City in August, hours before reiterating his harsh immigration plans at a campaign rally in Arizona Reuters US election 2016: the race for the White House in pictures Bernie Sanders officially endorsed Hillary Clinton, saying his progressive vision for ‘a transformed America’ would be ’best served by the defeat of Donald Trump’ Reuters US election 2016: the race for the White House in pictures Khizr and Gazala Khan appeared at the DNC to slam Trump for his stance on Muslim immigration, citing the case of their son Humayun Khan, who was killed in combat while serving as a Captain in the US Army in Iraq US election 2016: the race for the White House in pictures Libertarian candidate Gary Johnson is doing better in polls than any third party candidate since Ross Perot, 20 years ago Nicholas Kamm/AFP/Getty US election 2016: the race for the White House in pictures Green Party candidate Jill Stein (centre) marches with supporters in Colorado AP US election 2016: the race for the White House in pictures Hillary Clinton and Virginia Senator Tim Kaine at a rally in Kaine's home state in July, days before Ms Clinton tapped him to be her running mate Getty US election 2016: the race for the White House in pictures Trump on the campaign trail with his vice presidential pick, Indiana governor Mike Pence AP US election 2016: the race for the White House in pictures Former Ukip leader Nigel Farage appears at a Trump rally in Mississippi in August, where he told the crowd that he 'wouldn't vote for Hillary Clinton if you paid me'.

Most people on boths sides do not expect the losing candidate to concede the race gracefully.

The poll surveyed 1,192 American adults online from 17 to 21 October. The results have a credibility interval of plus or minus 3.3 percentage points. The credibility interval for Democrats is 5.1 percentage points; for Republicans it is 5.5 points.