More shelling of Ukraines Zaporizhzhia nuclear power plant has been reported, with Ukraine and Russia again blaming each other for the attack.
Each side said there were 10 hits on the plants administrative office and fire station on Thursday.
UN Secretary General António Guterres warned the fighting could "lead to disaster" at Europes largest nuclear plant, seized by Russia in early March.
Ukraine warned that Russia may provoke the worlds worst nuclear accident.
On Wednesday, foreign ministers from the G7 group of industrialised nations said Russia must immediately hand back control of the plant to Kyiv.
The facility and its surrounding area in central-eastern Ukraine saw shelling last week, with Russia and Ukraine also accusing each other over that attack.
Ukraine says Russia has turned the site into a military base, launching attacks from there, knowing that Ukrainian forces are unlikely to retaliate.
Moscow denies the claim.
In a statement on Thursday, Ukraines nuclear agency Enerhoatom said that "Russian invaders again shelled the Zaporizhzhia plant and territories near the nuclear facility".
It said an administrative office near the welding area was hit, and the storage of radiation sources. There was a small fire on some nearby grass, but no injuries.
Enerhoatom added that the fire station located near the plant was also targeted.
Because of the shelling, it was impossible to change the personnel after their shift, so they had to continue work overtime.
But the situation was currently under control, Enerhoatom said.
The Russian-installed officials issued a mirroring statement, accusing Ukraine of carrying out the shelling.
They said Ukrainian forces were using multiple-launch rocket systems and heavy artillery. The claims by each of the side have not been independently verified.
Meanwhile, UN Secretary General Guterres warned: "Urgent agreement is needed at a technical level on a safe perimeter of demilitarisation to ensure the safety of the area".
Mr Guterres was speaking ahead of a UN Security Council crisis meeting over the issue in New York City.
In Kyiv, Ukrainian President Volodymyr Zelensky warned that "Russia may provoke the worlds worst nuclear accident... bigger than Chernobyl". He was referring to the 1986 disaster at the Soviet-build nuclear plant north of Kyiv.
Mr Zelensky said that such an accident would be tantamount to Russia using its nuclear weapons without conducting an actual nuclear strike.
The Zaporizhzhia plant is in the city of Enerhodar, in the south-east of Ukraine along the left bank of the River Dnieper (Dnipro in Ukrainian).
It consists of six pressurised water reactors and stores radioactive waste.
After seizing the complex, Russia kept its Ukrainian employees.
So far, UN nuclear watchdog officials have been unable to inspect the plant.
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Watch: Zaporizhzhia nuclear plant appears on fire after shelling (3 March 22).