Radiation at the Chernobyl nuclear power plant has exceeded control levels after Russia troops took control of the area, Ukraine has said.
Data from an automated system monitoring the exclusion zone show gamma radition levels more than 20 times those seen days earlier, analysts said.
Ukraine’s parliament said it was "currently impossible to establish the reasons for the change in the radiation background in the exclusion zone because of the occupation and military fight in this territory."
Russia's defence ministry claimed radiation levels coming out of the power plant are normal. Moscow said it would send paratroopers to the area to help secure the area.
But Claire Corkhill, professor of nuclear material degradation at the University of Sheffield and an advisor to the UK government, said it looked as though there had been "spike" in gamma radiation at the site.
"Around the Chernobyl power plant, the gamma radiation looks to have increased by around 20 times compared with a few days ago,” she said, though she added: "This appears to be based on a single data point, so caution should be taken not to over-interpret at this stage.”
Ms Corkhill added areas where radiation levels had increased most were near main routes in and out of the site, suggesting the increased movement of people or vehicles may have "disturbed" radioactive dust.
"This is backed up by the fact that in some areas of the zone, there is no increase at all," she added." "It shows that any release of radioactivity is probably highly localised."
The highly radioactive fuel material within the reactor at Chernobyl is buried deep within the base and underneath the new safe containment structure.
The professor concluded that it seemed "very unlikely" that radiation would be released from this area unless it was directly targeted.
Asked if the radiation poses a high risk, Ms Corkhill told The Independent: “I would say not very [much], especially to those outside of the exclusion zone.”
Experts at Ukraine’s nuclear agency did not provide exact radiation levels but also said the change was likely due to the movement of heavy military equipment in the area lifting radioactive dust into the air.
"Radiation starts to increase. It is not critical for Kyiv for the time being, but we are monitoring," the interior ministry said.
The US has said there are “credible” reports that staff at the nuclear site were being held hostage by Russian forces.
The still-radioactive site of the 1986 nuclear disaster lies some 100 kilometres from Kyiv.
Ukraine's neighbour Poland said it had not recorded any increase in radiation levels on its territory.
