Donald Trump has continued to float the possibility of challenging the results of the presidential election if there is a "questionable result," while promising to embrace the outcome "if I win".

Key points: Trump tells rally he will accept election outcome 'if he wins'

Trump tells rally he will accept election outcome 'if he wins' Trump later says he will accept a 'clear' result but reserves right to 'file a legal challenge'

Trump later says he will accept a 'clear' result but reserves right to 'file a legal challenge' The remarks have further deepened rifts in the Republican Party

The Republican presidential candidate used a rally in Ohio to attempt to explain his warning in the final debate that he might not accept the results come November 8.

But Mr Trump brushed off the likelihood of that happening with a confident prediction that "we're not going to lose".

"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," Mr Trump said.

After letting that vow hang in the air, he added: "If I win."

He later told the rally that he would "of course" accept a "clear" election result, but reserved the right to file a legal challenge if there is a "questionable result", clarifying his stance a day after he refused to promise he would trust the outcome if he loses.

"Of course, I would accept a clear election result, but I would also reserve my right to contest or file a legal challenge in the case of a questionable result," Mr Trump said.

Mr Trump's musings about hypothetical Election Day scenarios came as his campaign was reeling from widespread astonishment over his refusal to commit to the time-honoured American tradition of the election's loser acceding gracefully to the winner.

Mr Trump has warned repeatedly of impending, widespread voter fraud, despite no evidence to support him and plenty of evidence to the contrary.

Asked at the debate whether he would accept the outcome, Mr Trump said: "I will tell you at the time. I will keep you in suspense."

Democratic rival Hillary Clinton called the comments "horrifying", while several prominent Republicans also denounced Mr Trump's position, and some worried his stance might make it more difficult for his party to hold onto control of Congress.

'Concession is an act of respect for the American people'

Senator John McCain of Arizona, who lost the 2008 presidential election to Democrat Barack Obama, issued a strong statement saying that accepting the election result is "the American way".

Sorry, this video has expired Political analyst discusses the implications of Mr Trump's comments.

"I didn't like the outcome of the 2008 election. But I had a duty to concede, and I did so without reluctance," said Mr McCain, who has opened a poll lead in his Senate re-election race.

"A concession isn't just an exercise in graciousness. It is an act of respect for the will of the American people, a respect that is every American leader's first responsibility."

A few other Republicans, mostly those who have never backed Mr Trump, also rejected his comments.

Aides to House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell declined requests for comment.

Mr Trump's statement, the most controversial in a debate that at times descended into insults by both candidates, made banner headlines across the country and raised questions about whether he was committed to a peaceful transition of power, a cornerstone of American democracy.

Democrats jumped to ask Republican candidates whether they agreed with Mr Trump, who is making his first-ever run for public office and against Mrs Clinton, a former first lady, senator and secretary of state.

Mr Trump's vice presidential running mate, Governor Mike Pence of Indiana, said Mr Trump "will accept the outcome" because he is going to win.

In recent weeks, Mr Trump has stepped up allegations that the election is being rigged, though he has not offered specific evidence, and numerous studies have shown that the US election system, which is decentralised and run by the states, is sound.

Sorry, this video has expired US electoral map: Where the opinion polls are pointing

AP/Reuters