A "MAJOR" nuclear leak from a facility in Russia or Kazakhstan sent a radioactive cloud billowing over Europe, experts said yesterday.

French nuclear safety monitors IRSN reported that an accident at a fuel treatment or a radioactive medicine site is the likely cause behind higher-than-normal readings of irradiated particles across the continent in recent weeks.

4 This map shows where Iodine-131 particles were detected in February

It used weather patterns to track the nuclear winds back to their suspected source — an area south of the Ural mountains in rural Russia or northern Kazakhstan.

But worryingly, authorities in Russia have not reported any such incident and Kazakh officials have not commented, further shrouding the case in mystery.

IRSN director Jean-Marc Peres told Reuters: "Russian authorities have said they are not aware of an accident on their territory".

Ruthenium-106 is used in chemotherapy to treat eye tumours and is also used in radioisotope thermoelectric generators (RTGs), which power satellites.

4 Scientists ruled out the theory that a nuclear reactor had leaked into the atmosphere Credit: Getty - Contributor

4 Experts said the levels of radioactive material in Europe did not pose a threat to humans - but the initial leak was 'major' Credit: Getty - Contributor

The quantity of Ruthenium-106 released was "major", Peres added. He said if such an amount was released from a site in France it would lead to a kilometres-wide evacuation.

Nuclear scientists said last month there had been increase in levels of the isotope Ruthenium-106 detected in the air in Germany, Italy, Austria, Switzerland and France.

Thankfully, the levels detected do not pose a threat to humans, yesterday's IRSN announcement said.

4 Wind patterns suggest the source of the radioactive material found in Europe originated south of the Ural mountains in Russia or Kazakhstan Credit: Getty - Contributor

It also backs up earlier analyses that ruled out a nuclear reactor fault — which would have sent deadly levels of unstable radioactive material into the atmosphere.

Boffins were left baffled in February when radioactive Iodine-131 particles were detected in seven different European countries from Norway to Spain.

They too had their source narrowed down to Eastern Europe or Russia, but it was unclear what exactly produced the pollution.

Dome installed over Chernobyl to prevent further nuclear radiation leaks

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