Russian soldiers were likely exposed to radiation while they were occupying the area around the Chernobyl nuclear power station over the past four weeks, Ukrainian officials said on Friday.
Vehicles used by Russian forces would have raised radioactive dust clouds and soldiers also dug trenches in the most contaminated part of the site, Ukraine's nuclear agency Energoatom said.
The power station, the site of the world's worst nuclear disaster in 1986, was taken back under the control of Ukrainian forces on Thursday as Russia withdrew from areas north of the capital Kyiv.
"All the equipment at the Chernobyl power station is functioning. The control and radiation monitoring systems function as usual," power station chief Valery Seida said in a statement.
But he said the soldiers may have been exposed.
"The thick dust that their vehicles raised into the air and the radioactive particles it contains can easily penetrate into the Russians' organism through their lungs," Seida said.
Since they also dug trenches in the area, "it is entirely possible that they have been exposed to considerable levels of radiation", Energoatom said.
International Atomic Energy Agency (IAEA) director general Rafael Grossi said on Friday the agency had no confirmation of such reports and added that "the general radiation situation around the plant is quite normal".
However, he added the Russian withdrawal might have led to higher levels of "localised radiation" due to the movement of heavy vehicles, as was the case when Russia seized the site.
On Thursday the agency said it was "seeking further information in order to provide an independent assessment" of the reports that troops may have been contaminated.
Speaking to reporters in Vienna after a trip to Ukraine and Russia where he held talks with officials from both sides, Grossi also said the agency had "agreed separately with Russia and with Ukraine" on plans to send assistance missions to Ukrainian nuclear facilities.
Russia's capture of Chernobyl in the early days of its invasion of Ukraine, which began on Feb 24, raised worldwide fears over nuclear leaks.
Ukrainian Foreign Minister Dmytro Kuleba told reporters in Warsaw that Russia had shown "irresponsibility" in its actions around Chernobyl.
"Russia showed irresponsibility on all fronts, from its refusal to allow staff at the power station to fully carry out their duties to digging trenches in the contaminated area," he said.
Chernobyl's number four reactor exploded in 1986 and is now covered by a double layer of sarcophagus – the first built by the Soviet Union and another that was only completed in 2019.
The power station's three other reactors were successively closed down, with the latest shutting off in 2000.