Russia's meteorological service said on Tuesday it had measured pollution of a radioactive isotope at almost 1,000 times normal levels in the Ural mountains, the first official Russian data supporting reports that an accident had taken place.
But a representative of Rosatom nuclear corporation told AFP "there have been no incidents at nuclear infrastructure facilities in Russian Federation", adding that the concentration detected posed little threat.
The data appears to support a report by the French nuclear safety institute IRSN, which said on November 9 a cloud of radioactive pollution over Europe had indicated that an accident had taken place at a nuclear facility either in Russian Federation or Kazakhstan in the last week of September.
The Federal Service for Consumer Protection and Welfare, Rospotrebnadzor, also concluded that levels of Ruthenium-106 did not exceed acceptable limits.
"When the media got hysteric about some accident and cloud of ruthenium-106, we asked for explanations" from Rosgidromet and Rosatom, Russia's nuclear energy corporation, Savchenko wrote on his Facebook page.
France's IRSN ruled out the possibility of an accident in a nuclear reactor, saying the material it detected was more likely to have been released from a nuclear fuel treatment site or centre for radioactive medicine.More news: Russian billionaire arrested in France for tax evasion
More news: Broncos Paxton Lynch expected to start against Raiders
More news: Trump administration plans to end protected status for about 60000 Haitian immigrants
At the same time, the head of Rosgidromet said that the automatic monitoring system detected an increase in the concentration of Ru-106 not only in Russian Federation, but also in neighboring countries such as Poland, Romania, Bulgaria and Ukraine. In 1957, an explosion at Mayak led to one of the worst nuclear accidents in history.
"Another possibility is that materials containing ruthenium-106 were placed in a metal remelting furnace".
The confirmation largely matched the earlier assessment of French authorities, but Rosatom continues to dispute that it is responsible for the high radiation levels, although it operates a nuclear reprocessing plant in the area.
Evgeny Savchenko, the Chelyabinsk region's minister of public security, said that the regional administration had not received any official information about risky levels of radiation in September.
The Mayak facility in the southern Urals, which is under Rosatom's umbrella, also said the contamination "has nothing to do with Mayak's activities". It does not occur naturally.
It said there was no health risk.
"Based on these data, Greenpeace Russia will send a letter to the office of the public prosecutor to request an investigation into possible concealment of a radiation accident and for the release of information on the status of the environment", the NGO says.