Ukraine's state nuclear power company says offsite electricity supply to the Zaporizhzhia nuclear plant has been partly restored. The firm also says it decided to shut down the plant's only operating reactor.

Energoatom said on Sunday that one of the plant's power lines damaged by Russian shelling was restored to operational capacity on Saturday evening. The firm said this made it possible to use external power for the plant's in-house needs.

The plant has been under the control of Russian forces since early March. It is one of the largest nuclear power plants in Europe.

The plant lost all offsite power for its reactor cooling system earlier this month after shelling damaged all transmission lines linking it to the electricity grid. Ukraine and Russia are accusing each other of conducting such attacks.

Energoatom said that after losing external electricity supply, the plant's No.6 reactor has been operating "at a critically low capacity level" over the past three days to power the in-house needs.

But the firm now said it decided to shut down the reactor and "transfer it to the safest state -- cold shutdown."

The International Atomic Energy Agency said the Ukrainian side informed it that the reactor was shut down on Sunday morning after the power line linking the plant and a nearby thermal power station was restored.

Energoatom said the risk of the transmission lines being damaged again "remains high." It added in the event of that happening, the plant will use diesel generators to power its in-house needs.

The company said it is necessary to stop Russian shelling of the transmission lines and establish a demilitarized zone around the plant in order to prevent an emergency.