Its military intelligence agency announced the apparent drawdown on Telegram, but Russia has so far not commented.

There have been ongoing fears about a potential disaster at the facility in southern Ukraine since the Russians took it over last year.

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Both sides have accused each other of shelling near the plant, the biggest in Europe, prompting stark warnings from the international nuclear watchdog.

A pullout by the Russians could go some way to easing those concerns.

"According to the latest data, the occupation contingent is gradually leaving the territory of the Zaporizhzhia nuclear power plant," said Ukraine's GUR.

Among the first reported to have left were three staff from state nuclear firm Rosatom who were "in charge of the Russians' activities".

The GUR said Ukrainian staff who signed Rosatom contracts had also been told to leave and that military patrols around the plant and the nearby city of Enerhodar were also reducing.

It claimed remaining personnel had been told "in case of any emergency situation" to blame Ukraine - which held disaster drills near the power station on Thursday.

Sky's military analyst Sean Bell said it could "be a sign the Russians are preparing for battle and getting rid of any extraneous personnel".

However, he said the sooner the plant is "back in Ukrainian control and is no longer a pawn in this dangerous and unpredictable war, the better".

Bell added that a key concern would be the state the plant is left in, as Russia has a "track record of leaving a trail of devastation".

"[They] could be planning to destroy or damage large areas of vital infrastructure at the nuclear plant to create a major distraction for the oncoming Ukrainian forces," he warned.

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Kyiv earlier this month accused Russia of planning a "terrorist" attack at Zaporizhzhia involving the release of radiation.

Moscow denied the accusation, and on Friday foreign minister Sergei Lavrov dismissed it as "pure lies" and provocation.

TV footage of the disaster drills showed rescuers in protective gear, and vehicles being checked for radiation levels and being decontaminated.

Mock casualties were also seen being brought into a medical tent.