The leaders of Ukraine and its close European allies - the UK, France and Germany - have set out out five conditions for reaching a "just and lasting" deal to end the war with Russia.
In a joint statement after talks in London, Volodymyr Zelensky, UK Prime Minister Sir Keir Starmer, French President Emmanuel Macron and German Chancellor Friedrich Merz said they would "stand firmly with Ukraine".
The five conditions include a stop to the fighting, starting negotiations from the current position in the field as well as "robust" security guarantees for Ukraine.
The leaders reiterated the need for the US to be part of the process at a time when US President Donald Trump's focus has shifted to the war with Iran.
Back in December, the US pushed Russia and Ukraine to sign up quickly to a plan to end the war, which began with Russian President Vladimir Putin's decision in February 2022 to launch a full-scale invasion of its neighbour.
The warring sides have recently intensified attacks against each other, with Russia using missiles and drones to attack Ukrainian cities - and Ukraine displaying increased abilities to reach deep into Russian territory with new technology.
On Saturday, Ukrainian drones hit Russia's second-largest city, St Petersburg, as it hosted the final day of a major economic forum - an attack described as "unprecedented" by Russian authorities.
Days earlier, Kyiv had attacked the outskirts of the same city - some 1,000km (620 miles) from Ukraine - as Putin's flagship forum was getting started.
On the eve of the event, Zelensky sent an open letter to Putin calling for direct negotiations to end the war - an offer repeatedly rejected by the Russian leader. Putin said he would end the war only when Russia's goals had been met.
The three Western powers meeting at 10 Downing Street in London on Sunday constitute the so-called E3 group and are some of Kyiv's strongest allies. The UK and France lead the "coalition of the willing" initiative to provide security guarantees for Ukraine as part of any future peace process.
They welcomed Zelensky's letter to Putin and supported his call for "a direct dialogue between Ukraine and Russia - with active US and European participation".
In an apparent reference to Moscow's insistence that Ukraine give up its ambition to join the Nato defence alliance, they said Ukraine right "to choose its own security arrangements and alliances must be fully respected".
Before arriving in London, the Ukrainian leader accused Russia of a "vile" attack after Kyiv officials said a drone had struck a storage facility for spent nuclear fuel near the Chornobyl nuclear plant.
There were no injuries and a fire was put out with radiation levels remaining stable.
Separately, at least three people were killed in a Russian strike in a village outside Zaporizhzhia in the south of the country, authorities said.
Zaporizhzhia has come under relentless Russian attacks recently, with at least two people killed there on Saturday.
The Russian strike on Chornobyl "partially destroyed" a spent nuclear fuel storage building, according to Ukraine's state-owned nuclear operator, Enerhoatom.
The operator said there were no injuries, and a fire in the building was put out, adding that radiation remained at a normal level.
The body also criticised Moscow for what it called a deliberate threat to nuclear safety, in words echoed by Zelensky.
"Russia deliberately struck this particular nuclear infrastructure facility," Zelensky said in a post on X, describing the building as an "as extremely critical infrastructure facility" and the attack as "vile".
Chornobyl - known during the Soviet era as Chernobyl - is the world's worst non-military nuclear disaster. A catastrophic explosion in 1986 sent a plume of radioactive material into the air, triggering a public health emergency across Europe.
Last year, a Russian drone hit the protective shelter over its damaged nuclear reactor.
