Former US President Donald Trump says he has agreed to a televised debate with Vice President Kamala Harris scheduled for September 10 ahead of November's presidential election.

In the US presidential election, it is customary for candidates to take part in a televised debate and exchange opinions ahead of the voting day.

Trump made the announcement on social media on Tuesday. He said the rules will be the same as the last debate in June with President Joe Biden. Under one rule, the candidates were not allowed to bring pre-written notes onto the stage.

ABC News was due to sponsor the debate between Harris, a Democrat, and her Republican rival, Trump scheduled for September 10 in Pennsylvania, one of the key battleground states.

But media outlets reported that the rival camps were at odds over the rules. Trump questioned the fairness of ABC News and called for a debate hosted by a different TV network.

The Harris camp has not so far released an official statement.

US media outlets say the Harris campaign wants both candidates' microphones to be live throughout the broadcast, suggesting the debate rules have not yet been settled.

The debate is expected to mark the first face-off between Trump and Harris.