Rafael Grossi, head of the International Atomic Energy Agency (IAEA), has urged both sides to exercise restraint, warning of the “very real risk of a nuclear disaster.”

And foreign ministers from the Group of Seven leading industrialised countries on Wednesday demanded that Russia immediately hand back control of the plant to Ukraine, something Moscow seems unlikely to do.

There was no immediate comment from Russia on the Ukrainian allegations of a rocket attack on Marhanets and Reuters could not independently verify the allegations.

Moscow says it does not deliberately target civilians in what it calls its “special military operation” in Ukraine aimed at preemptively safeguarding its own security against expansion of the Nato military alliance.

Andriy Yermak, President Volodymyr Zelensky’s chief of staff, accused Russia of launching attacks on Ukrainian towns with impunity from the Zaporizhzhia nuclear power plant in the knowledge that it was risky for Ukraine to fight back.

“Eighty reactive rockets fired at residential buildings,” Yermak wrote on the Telegram messaging service, referring to the attack on Marhanets.

“The terrorist nation is continuing to fight against civilians. The cowardly Russians can’t do anything more so they strike towns ignobly hiding at the Zaporizhzhia atomic power station”, he wrote.

Ukraine, which accuses Moscow of waging an unprovoked imperial-style war of aggression, says around 500 Russian troops with heavy vehicles and weapons are stationed at the plant, where Ukrainian technicians continue to work.

Staff at Ukraine’s Zaporizhzhia nuclear plant ‘under Russian orders’

Russia says its forces are behaving responsibly and doing everything they can to ensure the facility’s safety. Moscow has accused Ukrainian forces of shelling the plant, something Kyiv denies.

Valentyn Reznychenko, governor of Ukraine’s central Dnipropetrovsk region, said on Wednesday that the Russian attack on Marhanets was carried out with 80 Grad rockets.

More than 20 buildings had been damaged in the town, which is located on the other side of the Dnipro river from the power plant, he said.

The same attack damaged a power line, leaving several thousand people without electricity, he added. A hostel, two schools, a concert hall, the main council building and other administrative buildings had been hit too, he said.

Images supplied by Ukrainian officials showed the rubble-strewn corridor of a school that had apparently been hit with its windows blown out and a residential building pierced by a rocket.

US accuses Russia of using Ukraine power plant as ‘nuclear shield’

The head of Ukraine’s state nuclear power firm on Tuesday warned of the “very high” risk of shelling at the Zaporizhzhia nuclear power plant and said it was vital Kyiv regained control of the facility in time for winter.

He said lines that connect the plant to the Ukrainian grid had been damaged and accused Russia of wanting to connect the facility to its power grid.

“The risk is very high” of shelling hitting containers storing radioactive material, he said.

United Nations chief Antonio Guterres on Monday demanded UN nuclear inspectors be given access to Zaporizhzhia, calling any attack on a nuclear plant “suicidal.”

Moscow has asked for IAEA chief Grossi to brief the UN Security Council on Thursday on Russia’s accusations that it is Ukrainian forces who have attacked the plant, diplomats said.

Britain, which is helping Ukraine with weapons, intelligence and training, said on Wednesday that it believed Russia had “almost certainly” established a major new ground force to support its war.

The new force, called the 3rd Army Corps, was based in the city of Mulino, east of Moscow, the British Defence Ministry said in a daily intelligence bulletin.

It said it thought Russia would struggle to build up the number of troops it needed however and that the new force was unlikely to play a decisive role in the war.

The origin of a series of explosions at a Russian airbase in Russian-annexed Crimea a day earlier remained contested, with Moscow saying ammunition stores had detonated and Ukrainian officials hinting Kyiv may have been responsible.

Two US newspapers cited unnamed Ukrainian officials as saying that Ukrainian special forces had carried out an attack on the airbase, which had resulted in the destruction of Russian military aircraft there.

Zelensky did not directly mention the blasts in his daily video address late on Tuesday but said it was right that people were focusing on Crimea.

“We will never give it up … the Black Sea region cannot be safe while Crimea is occupied,” he said, repeating his government’s position that Crimea would have to one day be returned to Ukraine.