KYIV - U.N. Secretary-General Antonio Guterres said on Friday that the electricity generated at the Russian-held nuclear power plant in Ukraine's southern region of Zaporizhzhia belonged to Ukraine and demanded that principle be fully respected.

Ukraine accused Russia earlier on Friday of planning a "large-scale provocation" at the vast nuclear plant and said Russian forces planned to disconnect the facility from the Ukrainian power grid and link it up to the Russian one.

Moscow and Kyiv have accused each other of shelling Europe's largest nuclear power plant, which was captured by Russia in March, but is still run by Ukrainian technicians. Only two of the facility's six reactors are working.

Guterres, asked about Russian plans to divert power to the Russian power grid, told reporters in the Black Sea port of Odesa that the plant should be demilitarised, a move that he said would resolve the problem.

"Obviously the electricity from Zaporizhzhia is Ukrainian electricity and it's necessary especially during the winter for the Ukrainian people. And this principle must be fully respected," he said.

Ukraine is bracing for its most difficult winter in more than 30 years of independence and preparing for a possible energy shortage that would be exacerbated by the nuclear plant being disconnected.

International aid officials have voiced concern that such a move by Russia could trigger more hardship in the eastern part of Ukraine, particularly, and prompt more people to flee abroad.

Russia has itself accused Ukraine of plotting a "provocation" at the sprawling nuclear plant.

(Reporting by Andrea Shalal; writing by Tom Balmforth; editing by Toby Chopra and Philippa Fletcher)