Washington DC - US President Donald Trump on Thursday said that Russian President Vladimir Putin had made "a very promising statement" on a possible Ukraine ceasefire, but added that "it wasn't complete."

Trump's comments came after Putin said he backed the idea of a 30-day ceasefire but had serious questions about it that he wanted to discuss with his US counterpart.

"He put out a very promising statement but it wasn't complete," Trump, who was meeting NATO chief Mark Rutte at the White House, told reporters when asked about Putin's remarks.

"I'd love to meet with him or talk to him. But we have to get it (a ceasefire deal) over with fast."

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Trump, whose special envoy Steve Witkoff arrived in Moscow on Thursday for talks on Ukraine, added that it would be "a very disappointing moment for the world" if Russia rejects the peace plan.

"A lot of the details of a final agreement have actually been discussed. Now we're going to see if Russia is there and, if not, it will be a very disappointing moment for the world," Trump said.

Trump also gave a glimpse of the negotiations for a longer-term peace after any ceasefire, including what territory Ukraine would have to give up to Russia.

"We have not been working in the dark. We've been discussing with Ukraine land and pieces of land that would be kept and lost," he said.

He added that there was also "a very big power plant involved – who's going to get the power plant?"

Trump did not name any specifics but the Zaporizhzhia nuclear power plant, currently held by Russia, is on the front lines of the fighting. It is Europe's largest nuclear power station.

Negotiations were complex because they were effectively "creating the edge of a country," Trump added.

Ukraine agreed to a US proposal for a 30-day ceasefire at talks in Saudi Arabia this week, bowing to pressure after a blowout argument between Trump and President Volodymyr Zelensky in the Oval Office on February 28.