Ukraine's President Volodymyr Zelensky has arrived in the UK for talks with top European allies.
The talks - hosted by Prime Minister Sir Keir Starmer in Downing Street - also involve French President Emmanuel Macron and German Chancellor Friedrich Merz.
The three Western powers 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.
Sunday's meeting in London comes as 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 - now in its fifth year.
Announcing his arrival in the UK on Sunday afternoon in a post on X, Zelensky said the main focus of the leaders' talks would be "our defence in the war, greater co-operation for the security of all of Europe in the area of air defence, and our shared view of diplomatic prospects".
"Europe must be part of the negotiations and must be strong," he added.
Earlier, 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.
On Saturday, Ukraine targeted St Petersburg and the surrounding area as the city hosted the final day of a major economic forum, in a drone 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 Russian President Vladimir Putin's flagship forum was getting started, sending a large plume of black smoke over the city's skyline.
In the four years since Moscow's invasion began, Ukraine has developed its defence sector, with Kyiv now able to regularly hit targets within Russia.
On Friday, Putin rejected a proposal by Zelensky for face-to-face talks on ending the war, saying he did not see any point in meeting the Ukrainian leader.
Zelensky sent an open letter calling for a direct negotiations, writing it would be "wrong to simply wait" for the conflict to once again become the focus of US attention.
Speaking at the economic forum on Friday, Putin refused the request for a meeting with Zelensky and reiterated his position that a truce would only allow Ukraine to regroup.
He said he would end the war only when Russia's goals had been met.
