Trump holds a campaign rally in Cleveland, Ohio Thomson Reuters WASHINGTON (Reuters) - Republican presidential candidate Donald Trump will "100 percent" accept the results of the U.S. election if it is fair, his son Eric Trump said on Sunday.

“I think what my father is saying is, 'I want a fair election,’” Eric Trump said on ABC's "This Week."

“If it’s a fair outcome, he will absolutely accept it. There’s no question about that."

With national opinion polls showing Clinton with an increasing lead over Trump ahead of the Nov. 8 election, Donald Trump has repeatedly said the election is being "rigged" against him. He has not offered evidence and numerous studies have shown that the U.S. election system, which is decentralized and run by the states, is sound.

At last week's debate with Democratic rival Hillary Clinton, Trump challenged a cornerstone of American democracy by refusing to commit to honoring the result of the U.S. election.

"What I'm saying is that I will tell you at the time. I'll keep you in suspense. OK?" Trump said.

In the aftermath of the debate, Trump said he would accept the election outcome "if I win."

Trump's campaign manager, Kellyanne Conway, also was pressed on Sunday on CNN's "State of the Union" on whether Trump would accept the election results.

“The system is rigged, especially against the little guy,” said Conway without directly responding to the question. She spoke of any challenges to the election results as "hypothetical."

The efforts by members of Trump's inner circle to downplay his remarks about the integrity of the election indicate he would come under significant pressure to accept the result if he were to lose.

Clinton and Trump will campaign on Sunday in the key swing states of Florida and North Carolina, where the latest polls show they are within only a few points of each other.

(Reporting by Ginger Gibson and Alana Wise; Editing by Bill Trott)