Powerful explosions from shelling have struck Ukraine’s Zaporizhzhia region, the site of Europe’s largest nuclear power plant.
The International Atomic Energy Agency (IAEA) said more than a dozen blasts shook the Russian-occupied facility on Sunday, damaging buildings and equipment.
Ukraine blamed Russia, saying it was trying to prevent the plant from partially restarting to deliver electricity to millions of Ukrainians who are without heat, power or water in the freezing cold.
Russia blamed Ukrainian forces.
The fighting in the region has raised the spectre of a nuclear catastrophe ever since Russian troops occupied the plant during the early days of the war.
Later in the day, the IAEA said the shelling had stopped and that its experts would assess the situation on Monday.
“There has been damage to parts of the site, but no radiation release or loss of power,” the agency said.
The IAEA's director general, Rafael Mariano Grossi, called the shelling “extremely disturbing,” and appealed to both sides to urgently implement a nuclear safety and security zone around the facility.
“Whoever is behind this, it must stop immediately," he said. “As I have said many times before, you’re playing with fire!”
Russia has been pounding Ukraine’s power grid and other infrastructure from the air, causing widespread blackouts and leaving millions of Ukrainians without heat, power or water as frigid cold and snow blankets the capital, Kyiv, and other cities.
Ukraine’s state nuclear power operator, Energoatom, said Russian forces were behind the shelling of the Zaporizhzhia plant, and that the equipment targeted was consistent with the Kremlin’s intent “to damage or destroy as much of Ukraine’s energy infrastructure as possible" as winter sets in.
Ukrainian President Volodymyr Zelenskyy said more than 400 Russian strikes had also hit his country's eastern regions on Sunday alone.
He said blackouts were scheduled Sunday night in 15 regions of Ukraine and the city of Kyiv. More blackouts were scheduled in every region for Monday.
On Saturday, UK prime minister Rishi Sunak made a surprise visit to Ukraine - his first as leader.
He met with Mr Zelenskyy in Kyiv, where he praised his Ukrainian counterpart for his handling of the crisis, and pledged a £50 million defence aid package to aid his forces' efforts.
Mr Sunak said he was “humbled” to be in Ukraine as he held his first face-to-face meeting with Mr Zelenskyy.
The British PM laid flowers at a memorial for the war dead and lit a candle at a memorial for victims of the Holodomor famine, before meeting emergency personnel at a fire station.
Mr Zelenskyy later tweeted his thanks to Mr Sunak, writing: “With friends like you by our side, we are confident in our victory. Both of our nations know what it means to stand up for freedom."
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