Prime Minister Boris Johnson has vowed to seek an emergency UN Security Council meeting in a bid for a ceasefire following Russia's attack on a Ukrainian nuclear power station.
Mr Johnson made the promise during an early morning phone call with Ukrainian President Zelensky after the nuclear plant in the south-eastern city of Zaporizhzhia was shelled overnight.
The power station – the largest in Europe – caught fire after it was attacked by Russia.
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While the reactor is under renovation, according to the power plant’s spokesman, it still contains nuclear fuel.
Mr Johnson said that the "reckless actions of President Putin could now directly threaten the safety of all of Europe."
Downing Street said the situation in Zaporizhzhia was “gravely concerning”.
In a statement sent to PA News Agency, a spokeswoman for the PM’s office said: “Both leaders agreed that Russia must immediately cease its attack on the power station and allow unfettered access for emergency services to the plant.
“The Prime Minister said the reckless actions of President Putin could now directly threaten the safety of all of Europe.
"He said the UK would do everything it could to ensure the situation did not deteriorate further.
“The Prime Minister said he would be seeking an emergency UN Security Council meeting in the coming hours, and that the UK would raise this issue immediately with Russia and close partners.
“Both leaders agreed a ceasefire was crucial.”
Several hours later, Ukrainian emergency services announced on social media that the fire had been extinguished.
Firefighters added that the blaze had been in the educational and training building of the plant and no-one was harmed.
Earlier in the night, the plant’s spokesman Andriy Tuz told Ukrainian television that shells were falling directly on the Zaporizhzhia plant and had set fire to one of the facility’s six reactors.
Firefighters could not get near the fire because they were being shot at, Mr Tuz said.
According to the International Atomic Energy Agency (IAEA) the fire did not cause a change in the plant’s radiation level.
Nor had the shelling or fire caused any damage to “essential” equipment.
The agency added that its Director General Mariano Grossi was in touch with Ukraine’s Prime Minister Denys Schmygal and the Ukrainian regulator and operator about the situation.
The agency later tweeted to say it had put its incident and emergency centre in “full 24/7 response mode due to serious situation at Zaporizhzhia”.
It comes ahead of crisis talks between Western ministers as Vladimir Putin steps up his assault on Ukraine’s cities.
Liz Truss will join fellow foreign ministers from Nato and the European Union for a series of meetings in Brussels as the allies show their support for Ukraine.
Meanwhile, Home Secretary Priti Patel is visiting Poland’s border with Ukraine to highlight the visas on offer to those fleeing the conflict who have relations in Britain.
UN refugee agency figures show more than a million people have fled the country, a figure which could rise to four million as the war rages on.
