Donald Trump has again declined to commit to a peaceful transition of power if he loses November's US presidential election.

The president has for several months been pressing a campaign against mail-in voting in the poll by tweeting and speaking out critically about the practice, which has been encouraged by more states as a way of keeping voters safe amid the coronavirus pandemic.

"We're going to have to see what happens," Mr Trump told reporters in response to a question about whether he would commit to a peaceful transfer of power.

"You know that I've been complaining very strongly about the ballots, and the ballots are a disaster."

Mr Trump has baselessly claimed widespread mail voting will lead to massive fraud, despite the five states that routinely send mail ballots to all voters having seen no significant fraud.

On Wednesday he appeared to suggest that if states got "rid of" the unsolicited mailing of ballots there would be no concern about fraud or peaceful transfers of power.

He said: "You'll have a very peaceful - there won't be a transfer frankly. There'll be a continuation. The ballots are out of control, you know it, and you know, who knows it better than anybody else? The Democrats know it better than anybody else."

Mr Trump similarly refused to commit to accepting the results during an interview in July and made similar comments ahead of the 2016 election.

"I have to see. Look ... I have to see," he told Chris Wallace during a wide-ranging July interview on Fox News Sunday in July. "No, I'm not going to just say yes. I'm not going to say no, and I didn't last time either."

Joe Biden's campaign responded on Wednesday, as it did after Trump's July comments, by saying: "The American people will decide this election. And the United States government is perfectly capable of escorting trespassers out of the White House."

It is highly unusual that a sitting president would express less than complete confidence in the American democracy's electoral process.

But Mr Trump four years ago, when in the closing stages of his race against Hillary Clinton, also declined to commit to honoring the election results if the Democrat won.

Meanwhile, the President took a swipe at the Duchess of Sussex on Wednesday after she and husband Harry participated in a Time 100 video urging Americans to vote.

Meghan, an American, says in the video that every four years elections are referred to as the most important election of our lifetime. "But this one is," she stressed. "When we vote, our values are put into action and our voices are heard."

Harry called on Americans to "reject hate speech, misinformation and online negativity".

Neither mentioned Mr Trump or his Democratic challenger, Joe Biden, by name but some have interpreted their comments as critical of the president.

Mr Trump was asked about the video during a White House press conference, with the reporter saying the couple "essentially encouraged people to vote for Joe Biden".

"I'm not a fan of hers and I would say this, and she probably has heard that, but I wish a lot of luck to Harry. He's going to need it," Mr Trump replied.

The couple recently moved into a California home after announcing they were quitting royal duties and moving to North America, citing what they said was unbearable intrusion and racist attitudes from the British media.