Zaporizhzhia -- Europe's largest atomic power complex that was occupied by Russia early in its offensive -- has in recent days been the scene of military strikes that have damaged several structures, forcing the shutdown of a reactor.

As Russia and Ukraine blamed each other for the attacks, the head of the UN nuclear watchdog, the International Atomic Energy Agency (IAEA) warned on Saturday of "the very real risk of a nuclear disaster."

On Sunday, Russian occupation authorities in the city of Energodar where the plant is located said that overnight, "the Ukrainian army carried out an attack with a cluster bomb fired from an Uragan rocket launcher."

The projectiles fell within 400 metres of a working reactor," Russia's TASS state news agency quoted them as saying.

The strike damaged some administrative buildings and fell in a "zone storing used nuclear fuel".

The information could not be independently verified.

Russian troops have occupied the Zaporizhzhia plant since the early days of their offensive and Kyiv has accused them of storing heavy weapons there.

Moscow has accused Ukrainian forces of targeting the plant.

The plant's Ukrainian operator, Energoatom, said on Saturday that the strikes carried out on Friday had "caused a serious risk for the safe operation of the plant".

The strikes had damaged a power cable, forced one of the reactors to stop working and "seriously damaged" a station containing nitrogen and oxygen as well as an auxiliary building, said Energoatom.