Donald Trump says both Russian leader Vladimir Putin and Ukrainian President Volodymyr Zelenskiy expressed a desire for peace in separate phone calls with him, ordering top US officials to begin talks on ending the war in Ukraine.

The conversations came after the US president's defence secretary earlier said Kyiv would have to give up its long-held goals of joining the NATO military alliance and regaining all of its territory seized by Russia, signalling a dramatic shift in Washington's approach to the conflict.

After speaking with Putin for more than an hour, Trump said the Russian leader, who launched a full-scale invasion of Ukraine in 2022, wants the war to end, and they discussed "getting a ceasefire in the not-too-distant future".

"He wants it to end. He doesn't want to end it and then go back to fighting six months later," Trump told reporters in the Oval Office.

"I think we're on the way to getting peace. I think President Putin wants peace, President Zelenskiy wants peace and I want peace. I just want to see people stop getting killed," he added.

Trump has long said he would quickly end the war in Ukraine, without spelling out exactly how he would accomplish this.

With AAP.