Russian troops have handed control of the Chernobyl nuclear power plant back to Ukrainians and left the heavily contaminated site more than a month after seizing control of it.

The Ukrainian state nuclear company said on Thursday that all of the Russian forces occupying the power station had withdrawn from the territory surrounding the defunct facility.

“According to the staff of the Chernobyl nuclear power plant, there are now no outsiders on site,” Energoatom said in an online post. The state-owned firm had earlier said most troops had gone, leaving only a small number behind.

Energoatom said the pullout at Chernobyl came after soldiers received "significant doses" of radiation from digging trenches in the forest in the exclusion zone around the closed plant, although there was no independent confirmation of that.

The withdrawal took place amid growing indications the Kremlin is using talk of de-escalation in Ukraine as cover while regrouping, resupplying its forces and redeploying them for a stepped-up offensive in the eastern part of the country.

Russian forces have also retreated from the nearby town of Slavutych, where workers at Chernobyl live, the company said.

In a separate post, Energoatom said the Russian side had formally agreed to hand back to Ukraine the responsibility for protecting Chernobyl. It shared the scan of a document signed by people it identified as a senior staff member at Chernobyl, the Russian military official assigned to guarding Chernobyl.

Reuters could not immediately verify the authenticity of the document.

Ukraine has repeatedly expressed safety concerns about Chernobyl and demanded the withdrawal of Russian troops, whose presence prevented the rotation of personnel for a time.

Earlier this week, workers at the site told Reuters that Russian soldiers had driven without radiation protection through the Red Forest, the most radioactively contaminated part of the zone around Chernobyl, kicking up clouds of radioactive dust.

Asked to comment on the accounts from Chernobyl staff, Russia's defence ministry did not respond.

Energoatom said that as a result of their concerns about radiation, "almost a riot began to brew among the soldiers," suggesting this was the reason for their unexpected departure.

The IAEA said it had not been able to confirm the reports of Russian forces receiving high radiation doses.

Reports in Belarus suggest minibus-loads of Russian soldiers have sought medical attention for “acute radiation poisoning” at a clinic in the country after leaving Chernobyl.

At least seven minibuses of Russian soldiers have arrived at the clinic this week, according to a Belarusian news Telegram channel.

Anton Motolko, a Belarusian photographer, shared a photo of a medical vehicle that he said was transporting Russian troops in Belarus.

Russia occupied the plant hours after Putin launched his invasion of Ukraine on 24 February. The plant’s Ukrainian staff have continued to oversee the safe storage of nuclear waste, reportedly working at gunpoint.

Plant workers have also been safeguarding the reactor, which exploded in 1986 in a nuclear disaster considered to be the worst in history.

Ukraine has repeatedly expressed safety concerns about Chernobyl and the surrounding Red Forest, which had been affected by wildfires. Officials have warned that another explosion or forest fire would see radiation levels spike.

Kyiv demanded Russian troops, whose presence prevented the rotation of the plant’s personnel for a period of time, to withdraw from the plant.

Earlier on Thursday, the head of Energoatom urged the United Nations nuclear watchdog to help ensure Russian nuclear officials do not interfere in the operation of Chernobyl as well as the Zaporizhzhia nuclear power plant, which is also occupied by Putin’s troops.

Moscow has denied that its forces have put the Ukrainian nuclear facilities at risk.