A cloud of radioactive pollution spread over Europe after a possible "accident" at a nuclear facility in Russia or Kazakhstan, French nuclear safety officials confirmed on Friday.

France's nuclear safety institute, IRSN, picked up faint traces of ruthenium 106, a radioactive nuclide that is produced when atoms are split in a nuclear reactor and which does not occur naturally, in three of its 40 monitoring stations late September.

Faint traces were also detected in Germany, Austria, Italy and Switzerland.

There has been no impact on human health or the environment in Europe, a French official stressed, but he added that detection of such a cloud was "absolutely not normal".

IRSN, the technical arm of the French nuclear regulator, said in a statement it could not pinpoint the location of the release of radioactive material but that based on weather patterns, the most plausible zone lay south of the Ural mountains, between the Urals and the Volga river. This could indicate Russia or possibly Kazakhstan, it said.