Donald Trump has refused to publicly commit to accepting the results of the upcoming White House election.

The US President said it is 'too early' to make such an iron-clad guarantee, echoing a similar threat he made weeks before the vote four years ago.

His comments came as he scoffed at polls showing him lagging behind Democratic rival Joe Biden.

“Look … I have to see,” Mr Trump told moderator Chris Wallace during a wide-ranging interview on Fox News.

READ MORE: Donald Trump hits out ‘fake’ Fox News poll showing Joe Biden leading presidential race

He added: “No, I’m not going to just say ‘yes’. I’m not going to say ‘no’, and I didn’t last time either.”

The Biden campaign responded: “The American people will decide this election. And the United States government is perfectly capable of escorting trespassers out of the White House.”

The president contends that a series of polls that show his popularity eroding and Mr Biden holding an advantage are faulty. He believes Republican voters are under-represented in such surveys.

“First of all, I’m not losing, because those are fake polls,” Mr Trump said in the recorded interview, which aired on Sunday.

“They were fake in 2016 and now they’re even more fake. The polls were much worse in 2016.”

The 74-year-old president also stuck to a campaign charge that Mr Biden, 77, is unable to handle the rigours of the White House because of his age.

As for polls showing the incumbent is trailing, Mr Trump noted he was thought to be behind for much of the 2016 contest. “I won’t lose,” he predicted.