Energoatom said Moscow's troops had "repeatedly shelled" the site of the plant in southern Ukraine over the past day, whilst Russia' defence ministry claimed Kyiv's troops were responsible.

"As a result of periodic shelling, the infrastructure of the station has been damaged, there are risks of hydrogen leakage and sputtering of radioactive substances, and the fire hazard is high," Energoatom said on Telegram.

The agency said that as of midday Saturday (0900 GMT) the plant "operates with the risk of violating radiation and fire safety standards".

Russia's defence ministry said Ukrainian forces "shelled the territory of the station three times" in the past day.

"A total of 17 shells were fired," the ministry said in a communique.

The Zaporizhzhia facility was seized by Russian troops in the opening weeks of the February invasion and has remained on the front line ever since.

Kyiv and Moscow have traded accusations over shelling in the vicinity of the complex, located in the city of Energodar.

On Thursday, the plant was cut off from Ukraine's national power grid for the first time in its four-decade history due to "actions of the invaders", Energoatom said.

Ukrainian President Volodymyr Zelensky said the power cut was caused by Russian shelling of the last active power line linking the plant to the network.

It came back online on Friday afternoon but Zelensky warned "the worst case scenario ... is constantly being provoked by Russian forces".

The International Atomic Energy Agency (IAEA) is urging for a mission to the plant "as soon as possible to help stabilise the nuclear safety and security situation there".