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.

With Russia and Ukraine blaming 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 Energodar city 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".

However Ukraine's state nuclear enegry company Energoatom that operates the plant said the "Russian military keeps committing acts of nuclear terrorism" at the site.

"Yesterday ... the Russian occupiers once again fired rockets at the site of the Zaporizhzhya nuclear power plant and the town of Enerhodar," a company statement said.

"One... employee was hospitalised with shrapnel wounds caused by the explosion," it added.

The company accused the Russians of aiming at spent fuel casks, which are stored in the open near the site of shelling.

"Three radiation monitoring detectors around the ... site were damaged," the statement said adding that as a result radiation detection was impossible.

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.

Energoatom had on Saturday said strikes on Friday had "caused a serious risk for the safe operation of the plant", damaging a power cable and forcing the shutdown of one of the reactors.

The operator on Sunday called for the withdrawal of Russian troops from the site and for it to be declared a demilitarised zone.