Following five hours of talks on Sunday, negotiations between Ukraine's President Volodymyr Zelensky and United States representatives on a possible Russia-Ukraine peace deal resumed in Berlin, Germany on Monday, after Zelensky said Kyiv was willing to drop its bid for NATO membership in exchange for US and European security guarantees.

Talks continued at the German Chancellery after US envoy Steve Witkoff said Sunday that "a lot of progress was made" in discussions toward a potential agreement on ending Europe's deadliest conflict since World War II.

Zelensky's statement on NATO membership marked a retreat from his earlier stance that Ukraine should join the military alliance, whose expansion over the last three decades is cited by Moscow as one reason for the 2022 outbreak of conflict.

"From the very beginning, Ukraine's desire was to join NATO, these are real security guarantees. Some partners from the United States and Europe did not support this direction," Zelensky told reporters on Sunday.

"Article 5-like guarantees from the United States and from European partners, as well as from other countries — Canada, Japan ... would provide an opportunity (to prevent further conflict)," Zelensky said. This was "already a compromise on our part", he added.

Zelensky was expected to meet United Kingdom Prime Minister Keir Starmer, Germany's Chancellor Friedrich Merz and other European leaders in Berlin later on Monday.

Reuters reported that it remained unclear how much progress had been made on key questions, including the future of Ukrainian territory, and to what extent the Berlin talks might sway Russia toward a ceasefire.

On Monday, the Kremlin said Ukraine's non-accession to NATO is a core issue in negotiations over a potential peace settlement. "Naturally this issue is one of the cornerstones and, of course, it is subject to special discussion," Kremlin spokesman Dmitry Peskov told reporters. Peskov added that Russia expects a US update after the Berlin talks.

The talks take place in a pivotal week for the European Union, with a summit on Thursday set to decide whether the bloc backs a major loan to Ukraine using frozen Russian central bank assets.

"The most important thing for us is now to ensure we can finance Ukraine," said Denmark's Foreign Minister Lars Lokke Rasmussen in Brussels.

"We must take a decision to ensure that Ukraine is in a position to continue its freedom fight and to show the rest of the world that Europe is a strong player. Otherwise we will give in to the picture painted by the American president, that Europe is weak."

Finland's President Alexander Stubb, who met Zelensky on Monday ahead of the continuing US negotiations, sounded a tentatively hopeful note.

"I think we are at a critical moment in negotiations for peace," he said on Sunday. "And at the same time, we're probably closer to a peace agreement than we have been at any time during these four years."

Stubb said there were three key documents being prepared in the talks: a framework for a 20-point peace plan, one on security guarantees for Kyiv, and a third on Ukraine's reconstruction.

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