The UK will on Monday host European ministers for "critical" talks on "repelling Russian aggression", two days after Ukraine's allies demanded that Moscow accept a ceasefire.
Representatives from France, Germany, Italy, Poland, Spain and the EU will join Foreign Secretary David Lammy in London for a meeting of the so-called "Weimar+" group.
The coalition was set up in February in response to shifting US policy towards the war between Ukraine and Russia, and European security in general under President Donald Trump.
The meeting follows Saturday's visit by the leaders of France, Germany, Poland and the UK to Kyiv, where they called for Russia to agree to an unconditional 30-day ceasefire to allow for peace talks -- a proposal they said was backed by the US.
Russian President Vladimir Putin on Sunday proposed direct negotiations with Ukraine in Istanbul on May 15, but did not respond to the European call for a 30-day ceasefire.
Ukrainian President Volodymyr Zelensky said he would be prepared to meet Putin in Turkey, but did not say whether he would still attend if Russia refused the European proposal.
The London meeting, where Lammy is expected to announce further sanctions targeting those backing Russia's invasion, will be the sixth gathering of the Weimar+ group and the first hosted by the UK.
'Existential' challenge
The talks will cover "repelling Russian aggression and bolstering European security", said the UK Foreign Office.
They will focus on "both our joint efforts to strengthen European security and securing a just and lasting peace for Ukraine", it added.
Lammy will be joined by his German, Spanish and Polish counterparts, while France will be represented by its minister for Europe Benjamin Haddad.
The EU's top diplomat Kaja Kallas will also attend.
European leaders are "facing a once-in-a-generation moment for the collective security of our continent", said Lammy.
"The challenge we face today is not only about the future of Ukraine – it is existential for Europe as a whole," he said ahead of the talks.
"I have brought our friends and partners to London to make clear that we must stand together, allied in our protection of sovereignty, of peace and of Ukraine," he added.
Ceasefire plan
European leaders have reacted with scepticism to Putin's proposal for direct talks in Istanbul, with French President Emmanuel Macron warning that he was merely trying "to buy time".
"An unconditional ceasefire is not preceded by negotiations, by definition," he told reporters as he stepped off a train in the Polish city of Przemysl on his return from Ukraine.
He reiterated his position in a statement from the Elysee later Sunday, insisting on "necessity for a ceasefire" before talks between Putin and Zelensky.
In a phone call with Lammy on Sunday, US Secretary of State Marco Rubio said Washington's "top priority remains bringing an end to the fighting and an immediate ceasefire", State Department spokeswoman Tammy Bruce said.
Kyiv and its allies had feared that Trump was pivoting towards Moscow because he had clashed with Zelensky. But Trump has recently expressed growing impatience with Putin.
By James PHEBY/AFP
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