Republican presidential nominee Donald Trump said he will debate Democratic US Vice President Kamala Harris on Fox News on September 4, in a post on Truth Social late on Friday, though the Harris campaign did not confirm the event.

"Rules will be similar to the rules of my debate with Sleepy Joe, who has been treated horribly by his party, but with a full arena audience," Trump said, referring to President Joe Biden, who has since dropped his reelection bid.

Fox News did not immediately respond to a request for comment.

Trump's statement came right after the Democratic National Committee (DNC) launched an advertising campaign on Friday taunting him by saying "the convicted felon is afraid to debate" and questioning whether that is due to his stance on abortion.

After Biden dropped out of the race on July 21 and backed Harris, Trump said he would not debate her because she was not the official candidate.

On Friday, Harris secured the delegate votes needed to clinch the Democratic nomination.

Trump's post was removed for a few minutes before being reposted, with Trump deleting his proposal for a "major" town hall gathering on the same date if Harris was "unwilling or unable to debate".

Harris had responded last month that she was "ready" after Fox News proposed the presidential debate between the two candidates on September 17.

Trump said the debate would take place in the battleground state of Pennsylvania with a "full arena audience." The first and only debate this year between Trump and Biden had no in-house audience.