US and Ukrainian officials held what both sides called productive talks on Sunday about a Russia peace deal, with Secretary of State Marco Rubio expressing optimism about progress despite challenges to ending the more than 3-year-long war.

Rubio met with a Ukrainian delegation led by a new chief negotiator in Florida, his home state, for talks that he said were meant to create a pathway for Ukraine to remain sovereign and independent.

"We continue to be realistic about how difficult this is, but optimistic, particularly given the fact that as we've made progress, I think there is a shared vision here that this is not just about ending the war," Rubio told reporters after the talks concluded.

"It is about securing Ukraine's future, a future that we hope will be more prosperous than it's ever been."

The discussions were a follow-up to a new set of negotiations that began with a fresh US blueprint for peace.

Critics said the plan initially favoured Russia, which started the conflict with a 2022 attack on Ukraine.

Special envoy Steve Witkoff and US President Donald Trump's son-in-law, Jared Kushner, were also present representing the US side.

Witkoff leaves on Monday for Moscow, where he is expected to meet Russian counterparts for talks this week.

"There's more work to be done. This is delicate," Rubio said. "There are a lot of moving parts, and obviously there's another party involved here... that will have to be a part of the equation, and that will continue later this week, when Mr Witkoff travels to Moscow."

Trump has expressed frustration at not being able to end the war.

He pledged as a presidential candidate to do so in one day and has said he was surprised it has been so hard, given what he calls a strong relationship with Russian President Vladimir Putin, who has largely resisted concessions to stop the fighting.

Trump's team has pressured Ukraine to make significant concessions itself, including giving up territory to Russia.

The talks shifted on Sunday with a change in leadership from the Ukrainian side.

A new chief negotiator, national security council secretary Rustem Umerov, led the discussions for Kyiv after the resignation on Friday of previous team leader Andriy Yermak, chief of staff to Ukrainian President Volodymyr Zelensky, amid a corruption scandal at home.

"Ukraine's got some difficult little problems," Trump told reporters on Air Force One on Sunday, referring to the corruption scandal, which he said was "not helpful."

He repeated his view that both Russia and Ukraine wanted to end the war and said there was a good chance a deal could be reached.

Umerov thanked the United States and its officials for their support.

"US is hearing us, US is supporting us, US is walking besides us," he said in English as the negotiations began.

After the meeting, he declared it productive. "We discussed all the important matters that are important for Ukraine, for Ukrainian people and US was super supportive," Umerov said. (Reuters)