The United States has offered to provide Nato-style security guarantees for Kyiv as US and European negotiators reported progress in talks on Monday to end the war with Russia, but a deal on territorial concessions remained elusive.

Envoys sent by US President Donald Trump made the unprecedented offer at talks with Ukrainian President Volodymyr Zelensky in Berlin, US officials said, but warned such a deal would not be on the table forever.

Moscow is yet to agree to any of the changes discussed in Germany and has not indicated any willingness to do so.

"We're trying to get it done," Trump said of an agreement to end the war, speaking at the White House after he called into a dinner involving the key officials in Berlin.

"We had numerous conversations with President Putin of Russia, and I think we're closer now than we have been ever and we'll see what we can do," Trump added.

European leaders cautiously welcomed the Trump administration's apparent shift on security guarantees for Ukraine.

"For the first time since the war began, the possibility of a ceasefire is conceivable," said German Chancellor Friedrich Merz, who hosted the meetings, in a post on X.

"Today I had the feeling for the first time... that everyone was behaving like allies from one camp," Polish Prime Minister Donald Tusk told reporters on his plane after leaving Berlin.

"For the first time I heard from the mouths of American negotiators... that America would engage in security guarantees for Ukraine in such a way that the Russians would have no doubt that the American response would be military if the Russians attacked Ukraine again."

The US is leaning on Ukraine to withdraw its forces from the eastern Donetsk region, an official familiar with the matter said, in what would be a massive concession that could cause a ferocious backlash in Ukraine.

Calling the issue of territorial concessions "painful", Zelensky told reporters later: "Frankly speaking, we still have different positions."

But he said he believed US mediators would help find a compromise.

Kyiv's negotiators will continue consultations with US counterparts, he said, adding that Ukraine needed a concrete understanding on security guarantees, including the monitoring of a ceasefire, before making any decisions related to the war's front lines.

"I do not think that the (US) has demanded anything," Zelensky said. "I see us as strategic partners, so I would say that we have heard about the issue of territories in relation to Russia's vision or Russia's demands from the (US). We see this as demands from the Russian Federation."

US officials told reporters by conference call they had secured agreement on 90 percent of the issues.

Though longstanding territorial issues remain, one said, "we've got multiple different solutions to bridge the gap that we are suggesting to them".

Ukraine has said previously it would not cede territory to Russia, which has taken almost 20 percent of the country in its east and south since the start of the conflict in February 2022.

A European source briefed on the latest talks said Russia had not yet budged on its territorial demands. "The atmosphere is good but the goals remain quite far apart on the core," the source said.

Zelensky has been holding talks in Berlin with US envoy Steve Witkoff and President Donald Trump's son-in-law Jared Kushner as well as European leaders.

Kyiv is under intense pressure from Trump to make concessions to Russia.

A US official told reporters later that, under the deal being discussed in Berlin, Ukraine would receive security guarantees similar to those provided in Article 5 of the Nato treaty, which requires the alliance to come to the defence of any member that comes under attack. (Reuters)