"Obviously the electricity from Zaporizhzhia is Ukrainian electricity... This principle must be fully respected," the UN Secretary General said during a visit to the port of Odessa in southern Ukraine.

The Zaporizhzhia nuclear power plant was seized by Russian troops in March and recent fighting around it has raised the spectre of a nuclear incident comparable to Chernobyl.

Kyiv accused Moscow on Friday of planning to cut electricity produced in Zaporizhzhia.

"There is information that Russian occupying troops are planning to shut off the reactors and switch them from the output lines of the Ukrainian energy system," Ukrainian energy operator Energoatom said.

The operator also warned Russia was limiting staff access to the site.

Last week Energoatom said Russian forces were planning to re-route Zaporizhzhia's electricity to Crimea, annexed in 2014.

Both sides have this week accused the other of preparing "provocations" at the facility.

The plant -- the biggest in Europe -- was targeted by several strikes in recent days, increasing fears of a nuclear disaster. Both Kyiv and Moscow have accused each other over the attacks.

Guterres addressed those fears earlier this week in Lviv in western Ukraine saying that any damage to the plant would be akin to "suicide".

The plant, located near the Russian-annexed Crimean peninsula, has six of Ukraine's 15 reactors, and is capable of supplying power for four million homes.