Member countries of the International Atomic Energy Agency, an international organization that promotes peaceful use of nuclear energy, detected the radioactive isotope ruthenium-106 hovering above 14 European countries in early October, according to a statement from France's Nuclear Safety Authority.
The isotope was then detected in Tatarstan and then in southern Russian Federation, eventually reaching "all European countries starting in Italy and toward the north of Europe" from September 29, AFP cited Rosgidromet as saying.
Both Argayash and Novogorn villages, where the high levels of Ru-106 were detected, are located in close proximity (23km and 7km respectively) to the Mayak Production Association, one of the biggest nuclear facilities in Russian Federation.
The news bolsters worldwide reports that a ruthenium-106 leak originating in the Urals sent a radioactive cloud over Europe.
Austria first detected unusually large radiation levels on October 3, and Germany confirmed the levels the next day.
An incident in September-October at a cold war nuclear disaster site in Russian Federation is suspected to be the source of extremely high concentrations of radioactive material that spread over Europe, AFP reported on Monday.
In 1957, it was the site of the Kyshtym disaster, one of the worst nuclear accidents in history, which was kept secret by the Soviet Union for 30 years.
The Institute for Radioprotection and Nuclear Safety (IRSN) said on 9 November it had detected ruthenium-106 in France.
The French report said a nuclear reactor accident could not have been the source of the Ru-106 since other radioactive elements would also have been detected in the cloud.
"The measurement of its presence in the amounts reported suggest that any biological effects of exposure to this source are essentially similar to that of the normal, naturally occurring radiation background", he told Reuters. It had also said the levels recorded in Europe were of "no effect for human health and for the environment".
A mysterious cloud of radioactive material that hovered over Europe last month came from Russia, Russian weather monitoring data released today (Nov. 21) suggests.
The Institute of Nuclear Physics in Kazakhstan, which neighbours the southern Urals, has said there were no accidents at its scientific research reactor and no ruthenium 106 at its two disused testing areas in western Kazakhstan.
"Greenpeace will send a letter asking prosecutors to open an inquiry into potential concealment of a nuclear incident", the charity said in a statement.