Donald Trump has said he will accept the results of the election if he wins.
The Republican nominee added that he would accept a “clear” result – but reserved the right to challenge a “questionable” result.
Donald Trump appeared at a rally in Delaware, Ohio, speaking for the first time after the final debate with rival Hillary Clinton.
He has been heavily criticized for suggesting that he might not accept the election result.
Latest polls suggest Hillary Clinton is ahead nationally and in key battleground states.
Speaking in Ohio, Donald Trump said, grinning: “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.”
The billionaire also said: “I will accept a clear election result, but I will also reserve my right to contest and file a legal challenge in the case of a questionable result.”
During last night’s debate, when moderator Chris Wallace asked Donald Trump if he would accept losing to Hillary Clinton, the Republican nominee said he would “keep you in suspense”.
Donald Trump’s campaign manager, Kellyanne Conway, later insisted that the candidate had meant he would not concede until the “results are actually known”.
However the remark, which drew anger from some Republicans, is part of Donald Trump’s repeated claim that the election is “rigged” against him.
Donald Trump told the Ohio audience that the election was posing questions about “the fairness of our country”.
Former Republican presidential candidate Senator John McCain also released a statement implicitly criticizing Donald Trump’s debate comments.
John McCain, who lost to Barack Obama in 2008, said: “I didn’t like the outcome of the 2008 election. But I had a duty to concede, and I did so without reluctance.
“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.”
At the Ohio rally, Donald Trump also reiterated a claim he made during the debate against Hillary Clinton and President Obama, who he said were responsible for inciting violence at a Chicago rally earlier this year.
The crowd erupted into cheers of: “Lock her up!”
During the debate, Donald Trump called Hillary Clinton a “nasty woman”.
The Republican has trailed Hillary Clinton in the polls after facing damaging fallout over a video that emerged of him making inappropriate remarks about groping women.
When asked to address the allegations made against him by several women in the wake of the video, Donald Trump said the claims had been “largely debunked”.
Donald Trump’s comments come after a 10th woman came forward to accuse him of assault on October 20 at a news conference.
Karena Virginia said Donald Trump allegedly touched her breast at the US Open in 1998 and made offensive comments about her to a group of men.
Donald Trump and Hillary Trump are scheduled to appear at a charity dinner on October 20 in New York.