Wildfires threatened to stir radioactive particles left over from the 1986 Chernobyl nuclear disaster back into the air over western Russia, and authorities boosted forest patrols to keep the flames from contaminated areas.
Environmentalists and forest experts warned that the radioactive dust could be harmful, even though doses would likely be small.
"The danger is still there," said Vladimir Chuprov of Russian Greenpeace.
The Emergency Situations Ministry said at least six wildfires were spotted and extinguished this week in the Bryansk region — the part of Russia that suffered the most when the Chernobyl nuclear power plant's Reactor No. 4 exploded during a pre-dawn test on April 26, 1986, spewing radioactive clouds over much of western Soviet Union and northern Europe.
The ministry also had reported sporadic wildfires last week but said all were put out.
Radiation experts from Moscow determined that there has been no increase in radiation levels in the Bryansk area, on the border of Belarus and Ukraine, ministry spokeswoman Irina Yegorushkina said Wednesday.
The forest floor holds radioactive particles that settled after the Chernobyl disaster, which environmentalists warned could be thrown into the air by the fires raging across western and central Russia. The particles could then be blown into other areas by the wind, they said.
"A cloud may come up in the air with soot and spread over a huge territory," said Alexander Isayev of the Moscow-based Center for Forest Ecology and Productivity.
The most dangerous radioactive elements left by the Chernobyl accident are cesium and strontium, which with repeated exposure could raise the risks of cancers and genetic disorders, environmentalists said.
"There is a higher threat of cancers and future mutations, especially for children, [or] embryos, if a woman is pregnant," said Anton Korsakov, an environmental researcher at Bryansk State University.
A leading nuclear security scientist in Moscow, however, dismissed the danger. Even if forests in the most polluted areas catch fire, the amount of radiation would be many times lower than the natural background radiation, said Rafael Arutyunyan, director of the Moscow-based Institute for Safe Development of Nuclear Energy.
The Bryansk forestry service has increased patrols around the Bryansk forests, particularly in the southwest section affected by Chernobyl, agency chief Vladimir Rozinkevich said. "There is a danger, but we are controlling the situation," he said.
Emergency Situations Minister Sergei Shoigu acknowledged the danger last week but said Wednesday that the situation was not as difficult as in the areas around Moscow, where acrid clouds of smog from the fires have polluted the air.
Fires also have broken out in Ukraine, but the country's Emergency Situations Ministry said none have been reported in the areas contaminated by the Chernobyl accident.
There also has been no increase in radiation levels recorded in Ukraine, said Mykhailo Dovhych, deputy director of Ukraine's Central Geophysical Observatory, which monitors radiation levels.
In Vienna, the International Atomic Energy Agency said it had no comment on the radioactive dangers posed by the wildfires.