Ukraine narrowly escaped disaster during fighting at the weekend that rocked Europe's largest atomic power plant with a barrage of shells, some falling near reactors and damaging a radioactive waste storage building, the UN nuclear watchdog said.
It was not clear which side was responsible for the explosions at the Zaporizhzhia nuclear power station, which has been under Russian control since soon after it invaded Ukraine on February 24.
Whoever fired on the plant was taking "huge risks and gambling with many people's live,", said Rafael Grossi, director general of the International Atomic Energy Agency (IAEA).
"We were fortunate a potentially serious nuclear incident did not happen. Next time, we may not be so lucky," Grossi said late on Sunday in a statement, describing the situation as a "close call".
Repeated shelling of the plant during the war has raised concern about a grave disaster in the country that suffered the world's worst nuclear accident, the 1986 Chornobyl meltdown.
Radiation levels remained normal and there were no reports of casualties, the IAEA said. While there was no direct impact on nuclear safety and security systems, "the shelling came dangerously close to them", Grossi said.
The shelling comes as battles raged further east following troop movements from around Ukraine's recently recaptured Kherson, further south along the same Dnipro river on which Zaporizhzhia is located.
Russia's response to its military setbacks has included a barrage of missile strikes, many on power facilities that have left much of the country without electricity as winter sets in and temperatures drop below freezing.
Kyiv controls territory across the river from the power station, including the regional capital. The Zaporizhzhia plant itself and territory south of it fell to Russia in March.
Both sides traded blame for the latest shelling, as they have done repeatedly in recent months after attacks on the plant or near it.
Citing information provided by plant management, an IAEA team on the ground said damaged infrastructure included a radioactive waste and storage building, cooling pond systems, a cable to one of the reactors, and a bridge to another reactor and auxiliary buildings.
The team plans to conduct an assessment on Monday, Grossi said, but Russian nuclear power operator Rosenergoatom said there would be curbs on what the team could inspect.
"If they want to inspect a facility that has nothing to do with nuclear safety, access will be denied," Renat Karchaa, an adviser to Rosenergoatom's CEO, told the Tass news agency.
The Zaporizhzhia plant provided about a fifth of Ukraine's electricity before Russia's invasion, and has been forced to operate on back-up generators a number of times. It has six Soviet-designed VVER-1000 V-320 water-cooled and water-moderated reactors containing Uranium 235.
The reactors are shut down but there is a risk that nuclear fuel could overheat if the power driving the cooling systems is cut. Shelling has repeatedly cut power lines.
Russia's defence ministry said Ukraine fired shells at power lines supplying the plant. Ukraine's nuclear energy firm Energoatom said Russia's military shelled the site, accusing it of nuclear blackmail and actions that were "endangering the whole world".
In eastern Ukraine, Russian forces battered Ukrainian frontline positions with artillery fire, with the heaviest attacks in the Donetsk region, Ukraine's President Volodymyr Zelenskiy said in a video address on Sunday evening.
Russia withdrew its forces from the southern city of Kherson this month and moved some of them to reinforce positions in the eastern Donetsk and Luhansk regions, an industrial area known as the Donbas.
"The fiercest battles, as before, are in the Donetsk region. Although there were fewer attacks today due to worsening weather, the amount of Russian shelling unfortunately remains extremely high," Zelenskiy said.
"In the Luhansk region, we are slowly moving forward while fighting. As of now, there have been almost 400 artillery attacks in the east since the start of the day," he said.
Ukraine's military, in an early Monday update, confirmed heavy fighting over the previous 24 hours, saying its forces had repelled Russian attacks in the Donetsk region while Russian forces were shelling the Luhansk region in the east and Kharkiv in the northeast.
Reuters was not able to immediately verify the battlefield reports.
In the south, Zelenskiy said troops were "consistently and very calculatedly destroying the potential of the occupiers" but gave no details.
Kherson city remains without electricity, running water or heating.
Russia calls its invasion of Ukraine a "special operation" to demilitarize its neighbour. Kyiv and allies say the invasion is an unprovoked war of aggression.
Oleh Zhdanov, a military analyst in Kyiv, said that according to his information, Russian offensives were taking place on the Bakhmut and Avdiivka frontline in the Donetsk region, among others.
"The enemy is trying to break through our defences, to no avail," Zhdanov said in a social media video. "We fight back - they suffer huge losses."