Russia has said a leak of nuclear material detected over Scandinavia did not come from one of its power plants.

Nuclear safety watchdogs in Finland, Norway and Sweden said last week they had found higher-than-usual amounts of radioactive isotopes in the atmosphere.

A Dutch public health body said that, after analysing the data, it believed the material came "from the direction of western Russia".

It said the material could indicate "damage to a fuel element".

But in a statement, Russia's nuclear energy body said its two power stations in the north-west - the Leningrad NPP and the Kola NPP - were working normally and that no leaks had been reported.

"There have been no complaints about the equipment's work," a spokesperson for the state controlled nuclear power operator Rosenergoatom told Tass news agency.

"Aggregated emissions of all specified isotopes in the above-mentioned period did not exceed the reference numbers."

Radiation levels around the two powers stations "have remained unchanged in June", the spokesperson added.

Lassina Zerbo, executive Secretary of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) tweeted on Friday that its Stockholm monitoring station had detected three isotopes - Cs-134, Cs-137 and Ru-103 - at higher than usual levels but not harmful to human health.