US President Donald Trump has said that he was sending envoys Jared Kushner and Steve Witkoff to Moscow and Kiev with a plan to end the four-year-old Ukraine war.

It will be the first time that Trump's son-in-law Kushner and businessman friend Witkoff have visited war-torn Kiev since Trump returned to office last year with a vow to solve the conflict.

Both US envoys have previously visited Moscow, leading to accusations that they have taken Russia's side in negotiations.

"They're bringing with them a proposal to end the war," Trump told reporters on Friday when asked about the trip.

Trump would not say whether the plan involved Ukraine ceding territory as he has previously suggested but added: "We have an idea for peace."

"I sent Steve Witkoff and Jared Kushner, two great negotiators. They've done a great job, and we sent them over to see whether or not we can get something done. And there may be a good chance that we'll do it," he said.

The US leader blamed the war that began with Russian troops entering Ukraine in February 2022 on a "personality problem" between Russian President Vladimir Putin and Ukrainian President Volodymyr Zelenskyy.

Zelensky earlier said he had proposed observing a ceasefire with Russia while the US envoys visit Moscow and Kiev.

"There will be no airstrikes on our part, and Russia must reciprocally ensure a ceasefire -- without its own air strikes — for the duration needed to conduct these talks," Zelenskyy said in his evening address.

A senior Ukrainian official told AFP the two envoys would visit Kiev on Sunday. The Kremlin declined to comment on the matter.

A report in the US news outlet Axios said Kushner and Witkoff would travel on Friday, meet Putin at the Kremlin on Saturday, and then Zelensky in Kiev on Sunday.