British Prime Minister Keir Starmer and European allies spoke with US President Donald Trump about Ukraine as "intensive work" continues on the peace plan, PA Media and DPA reported, quoted by BTA.
Starmer, French President Emmanuel Macron and German Chancellor Friedrich Merz spoke with Trump at a time when US relations with Europe are under serious strain.
Starmer's office said all leaders agreed that this is a "critical moment" on the future of Ukraine and Euro-Atlantic security.
"The leaders discussed the latest news on the ongoing peace talks led by the US and welcomed their efforts to achieve a just and lasting peace for Ukraine and to end the killings," a spokesman for Starmer said.
"Intensive work on the peace plan is ongoing and will continue in the coming days," the spokesman added.
"They agreed that this is a critical moment – for Ukraine, its people and for the shared security of the Euro-Atlantic region," he added.
The three European leaders met Ukrainian President Volodymyr Zelensky on Monday in Starmer's Downing Street office 10 in London to discuss proposals to end the war, amid concerns that Washington's initial plan is based largely on Russian military objectives.
Zelensky's team is due to present its latest peace proposals to US negotiators, and tomorrow there will be a meeting of the "Coalition of the Willing" - countries led by Britain and France, which are ready to support Ukraine and deter Russia if there is a ceasefire.
Trump has criticised Ukraine's European allies, describing them as "weak" leaders of "decadent" countries who have failed to "produce" nothing while "the war just goes on and on".
The new US national security strategy, released earlier this month, says "the Trump administration is at odds with European officials who have unrealistic expectations for the war, rely on unstable minority governments, and many of whom trample on basic democratic principles to suppress opposition".
Zelensky said Ukraine would hold talks with the US on plans for post-war reconstruction and economic development. Kiev is also working on a 20-point document "that could set the parameters for ending the war," he added.
In connection with tomorrow's talks by the "Coalition of the Willing" Zelensky said: "This week can bring news for all of us and an end to the bloodshed".
Meanwhile, Ukrainian troops are repelling an unusually powerful mechanized attack on the strategic town of Pokrovsk, the Ukrainian military said on Monday, as quoted by Reuters.
For months, the Russian army has been attacking the town in small groups of infantry in an attempt to seize the logistics center that is key to Moscow's bid to control all of Donbas.
Russia says it has taken full control of Pokrovsk, which it calls Krasnoarmeysk. However, Kiev says it still controls the northern part of the town, where fierce street fighting is taking place, Reuters notes.