US President Donald Trump has defended special envoy Steve Witkoff as doing the "standard thing" after a leaked recording appeared to show him advising a Russian official on how to appeal to the president.

Trump told reporters on Wednesday he had not heard the audio, but that Witkoff was doing "what a dealmaker does" to "sell" the peace plan to both Russia and Ukraine.

The leaked call from last month emerged after days after a 28-point draft peace plan presented by the US largely reflected Russian positions on its full-scale war in Ukraine.

Witkoff has visited Moscow several times this year and will meet Russian President Vladimir Putin again next week. He has not held talks in Kyiv.

He has never gone to Kyiv in his role as special envoy, although other US officials have visited and US army secretary Dan Driscoll went to Kyiv this week and Trump says he will hold further talks with the Ukrainians.