KYIV: Ukraine's Russian-occupied Zaporizhzhia nuclear power station was operating on back-up diesel generators on Thursday after being disconnected from the Ukrainian power grid by Russian shelling, the Ukrainian nuclear energy company said.

Energoatom said the last remaining high voltage lines connecting the plant to the Ukrainian grid had been damaged in Wednesday's shelling, and that Moscow wanted to connect the plant to the Russian grid.

The facility in southern Ukraine, Europe's largest, has 15 days' worth of fuel to run the generators, Energoatom said.

Although the six reactors are shut down, they still need a constant supply of electricity to keep the nuclear fuel inside cool and prevent disaster.

"Yesterday ... the Zaporizhzhia NPP's (nuclear power plant's) last two high-voltage lines connecting it to Ukrainian power system were damaged. At 11:04 p.m., the station went into full blackout mode. All 20 diesel generators were switched on," it said in a statement on the Telegram messaging app.

"In the near future, they (Russia) will try to repair and connect the communication lines of the ZNPP in the direction of temporarily occupied Crimea and Donbas," said Energoatom, whose staff still operate the plant despite its occupation by Russian forces.

Russia did not immediately comment on the situation at the plant.

The facility, which provided about a fifth of Ukraine's electricity before Russia's Feb. 24 invasion, has been forced to operate on back-up generators a number of times since it was occupied by Russian forces soon after the war began.

Russia and Ukraine have blamed each other for shelling at the site that has damaged buildings and threatened a nuclear accident. The U.N. nuclear watchdog is pushing for a protection zone to be set up to prevent further shelling.