The head of the UN nuclear watchdog (IAEA) denounced "targeted" strikes at Ukraine's Russian-controlled Zaporizhzhia nuclear plant at the weekend. He says a team will be sent to inspect the site on Monday.
The International Atomic Energy Agency (IAEA) said more than a dozen blasts shook the Zaporizhzhia nuclear plant overnight on Saturday.
IAEA chief Rafael Grossi said the attacks were "extremely disturbing and completely unacceptable".
It was not clear which side was responsible for the explosions, some of which a team of experts from the agency on site had themselves seen, the IAEA said in a statement.
Speaking to French broadcaster BFMTV later Sunday, Grossi was clear that the strikes on the plant were no accident.
"The people who are doing this know where they are hitting. It is absolutely deliberate, targeted."
Citing information provided by plant management, an IAEA team on the ground said there had been damage to some buildings, systems and equipment, but none of them critical for nuclear safety and security.
"We were fortunate a potentially serious nuclear incident did not happen. Next time, we may not be so lucky," Grossi said, describing the situation as a "close call".
The IAEA is to send a team of experts to the plant, Europe's biggest nuclear facility, and which is currently controlled by Russian troops.
But Russian nuclear power operator Rosenergoatom said there would be curbs on what the team could inspect.
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"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.
Repeated shelling of the plant has raised concern about a grave accident just 500 kilometres from the site of the world's worst nuclear accident, the 1986 Chernobyl disaster.
The Zaporizhzhia plant provided about a fifth of Ukraine's electricity before Russia's invasion on 24 February, 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 but Ukraine's nuclear energy firm Energoatom accused Russia's military of shelling the site, saying the Russians had targeted infrastructure necessary to restart parts of the plant in an attempt to further limit Ukraine's power supply.
Attacks on infrastructure
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.
Ukraine's President Volodymyr Zelensky, in his daily address, said there had been nearly 400 Russian attacks in the east of the country alone on Sunday.
The toughest battles, he said, were in the eastern Donetsk region, one of those Russia now claims as its own. Fighting was also continuing in neighbouring Lugansk.
Teams were working around the clock to repair damage to the energy infrastructure wrought by Russia's artillery bombardments but "stabilisation blackouts" were nevertheless necessary in 15 regions, including Kyiv, he added.