Ukraine's nuclear agency and interior ministry said on Friday they were recording increased radiation levels from the site of the defunct Chernobyl nuclear power plant.
Experts at the state nuclear agency did not provide exact radiation levels but said the change was 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 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.