The UK is hosting European ministers today for "critical" talks on "repelling Russian aggression", two days after Ukraine's allies demanded that Russia accept a ceasefire.
Representatives from France, Germany, Italy, Poland, Spain and the EU are joining 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 US President Donald Trump.
Mr Lammy is expected to announce further sanctions targeting those backing Russia's invasion, his ministry said.
The meeting follows Saturday's visit by the leaders of France, Germany, Poland and the UK to Ukraine.
During the visit, the leaders - joined by the United States - called for Russia to agree to a 30-day ceasefire to allow for peace talks.
This is the sixth meeting of the Weimar+ group and the first hosted by the UK.
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.
Mr Lammy is being 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 is also attending.
'Existential' challenge
European leaders are "facing a once-in-a-generation moment for the collective security of our continent", said Mr 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.
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"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.
Yesterday, Russian President Vladimir Putin proposed direct negotiations with Ukraine in Istanbul on 15 May. He did not respond to the European call for an unconditional 30-day ceasefire starting from today.
Read more: European leaders agree on stronger Ukraine, differ on 'reassurance force'
Ukrainian President Volodymyr Zelensky said he would be prepared to meet Mr Putin in Turkey, but did not say whether he would still attend if Russia refused the 30-day ceasefire proposal.
French President Emmanuel Macron warned that Mr Putin 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, insisting on "necessity for a ceasefire" before talks between Mr Putin and Mr Zelensky.
The European leaders, together with Mr Zelensky, had pressed Russia in the Kyiv meeting on Saturday to accept the unconditional ceasefire, threatening Russia with new sanctions if it did not comply.
The United States and other countries back the proposal, they said.
Ukraine and its allies had feared that Mr Trump was pivoting towards Russia because he had clashed with Mr Zelensky. But Mr Trump has recently expressed growing impatience with Mr Putin.
