"The actions of the invaders caused a complete disconnection of the (Zaporizhzhia Nuclear Power Plant) from the power grid -- the first in the history of the plant," Energoatom said on Telegram.

The Zaporizhzhia plant -- Europe's largest nuclear facility -- has been occupied by Moscow's troops since the opening weeks of the war.

It has remained on the frontlines ever since, and in recent weeks Moscow and Kyiv have traded blame over shelling around the complex in southern Ukraine.

Energoatom said the plant was disconnected from Ukraine's national supply system after a power line was twice disconnected by fires at ash pits in an adjacent thermal power plant.

The three other power lines "were earlier damaged during terrorist attacks" by Russian forces, the operator said.

As a result, the two of the plant's six reactors still functioning "were disconnected from the network".

Energoatom said "start-up operations are under way to connect one of the reactors to the network".

Kyiv officials have said they believe Moscow has seized the station in order to divert power to the Crimean peninsula annexed by Russia in 2014.

Energoatom could not be immediately reached for comment on whether the supply had been diverted.