European and other Western leaders said on Saturday a U.S. peace plan was a basis for talks to end Russia's war in Ukraine but needed "additional work," part of Western efforts to eke out a better deal for Kyiv before a Thursday deadline.

Meeting on the sidelines of a G20 summit, European and other Western leaders scrambled to come up with a coordinated response to U.S. President Donald Trump's demand for Ukraine to accept his 28-point peace plan with Russia by Thursday.

Trump said in brief remarks later that his proposal was not his final offer, signalling potential room for adjustments, as Ukraine and its European allies stressed that the plan could serve as a foundation for negotiations but would require changes.

The European and other Western leaders agreed national security advisers from the E3 — France, Britain and Germany — would meet European Union, U.S. and Ukrainian officials in Geneva on Sunday for further discussions. Italy would also send an official, diplomatic sources said.

The U.S. plan, which endorses key Russian demands, was met with measured criticism in many European capitals, with leaders trying to balance praise for Trump for trying to end the fighting with recognition that some of the terms in his proposal are unpalatable for Kyiv.

"The initial draft of the 28-point plan includes important elements that will be essential for a just and lasting peace," said the leaders of the EU, Germany, France, Britain, Canada, the Netherlands, Spain, Finland, Italy, Japan and Norway.

"We believe therefore that the draft is a basis which will require additional work," they said in a statement.

"There are many things that cannot simply be an American proposal, which requires broader consultation," said French President Emmanuel Macron, adding that an agreement had to allow for peace for Ukrainians and "security for all Europeans."

The leaders met after President Volodymyr Zelenskyy said on Friday that Ukraine faced a choice of either losing its dignity and freedom or Washington's backing for the plan. He appealed to Ukrainians for unity, promising never to betray Ukraine.

That signal prompted European leaders to rally.

A German government source said they had met in a room in Johannesburg called "lion" and that the leaders had adopted the animal's "spirit" in talks to agree on a way to try to secure a better deal for Ukraine.

German Chancellor Friedrich Merz underlined the importance to Europe of supporting Ukraine.

"If Ukraine loses this war and possibly collapses, it will have an impact on European politics as a whole, on the entire European continent. And that is why we are so committed to this issue," Merz said on the sidelines of the G20 summit.

"There is currently an opportunity to end this war, but we are still quite a long way from a good outcome for everyone."

Zelenskyy appealed to his country for unity.

"Now, Ukraine can face a very difficult choice — either losing dignity or risk losing a major partner," he said in a speech to the nation on Friday. "I will fight 24/7 to ensure that at least two points in the plan are not overlooked – the dignity and freedom of Ukrainians."

On Saturday, he signalled that security guarantees were imperative for any deal to "ensure that nowhere in Europe or the world does the principle prevail that crimes against people and humanity, against states and nations, can be rewarded and forgiven."

On the frontline, one Ukrainian soldier, 33-year-old Vitalii Traikalo, questioned why Ukraine should be forced to give up territory after three years of grueling fighting to fend off Russian assaults.

"Are we defending our borders here just to give them away? What's the point of all this, of all these sacrifices?" he asked, while manning an artillery position near the eastern Ukrainian city of Pokrovsk.

On Friday, Trump threw down the gauntlet to Ukraine, saying Zelenskyy had until Thursday to approve his 28-point plan, which calls on Ukraine to cede territory, accept limits on its military and renounce ambitions to join NATO.

"He'll have to like it, and if he doesn't like it, then you know, they should just keep fighting, I guess," he said. "At some point he's going to have to accept something he hasn't accepted."

Recalling their fractious February meeting with Zelenskyy, Trump added: "You remember right in the Oval Office, not so long ago, I said, 'You don't have the cards.'"

In their statement, Western leaders said they were "concerned by the proposed limitations on Ukraine's armed forces, which would leave Ukraine vulnerable to future attack."

"We reiterate that the implementation of elements relating to the European Union and relating to NATO would need the consent of EU and NATO members respectively."

Sunday's meeting in Geneva now comes into focus, with European nations keen to suggest changes to Trump's plan, which Russian President Vladimir Putin described as the basis of a resolution to the conflict.