The International Atomic Energy Agency (IAEA) said on Saturday that the plant -- Europe's largest nuclear power station -- had lost its last source of external power after renewed shelling and was relying on emergency generators.

"Our team at Zaporizhzhia confirms the offsite power line lost yesterday was restored and ZNPP (the plant) is reconnected to the grid -- a temporary relief in a still untenable situation," IAEA head Rafael Grossi tweeted on Sunday.

Although the plant's six reactors are in cold shutdown, they require electricity for vital nuclear safety and security functions, including cooling.

Russian President Vladimir Putin ordered his government this week to take over operations at the power station in southern Ukraine, where fears of an atomic accident remain high.

Grossi was in Kyiv on Thursday to discuss setting up a protection zone around the site which has regularly come under fire with Ukraine and Russia blaming each other.

"A protection zone is needed now. I will travel to Russia and will see Ukraine's (President Volodymyr) Zelensky thereafter to establish the zone," Grossi added in his tweet on Sunday.

He has stressed the zone's main aim is "to avoid a nuclear accident at the plant, which remains a very, very clear possibility".

Electricity has been cut to the site several times since August.