Radioactive particles that were detected over northern Europe last week were likely emitted from a nuclear reactor, but the origin is still unknown, the International Atomic Energy Agency (IAEA) said on Friday in Vienna.
"Low levels of radioisotopes detected in Europe likely linked to a nuclear reactor," the agency wrote in Twittter.
The agency also published a statement in its website saying that "the recent detection of slightly elevated levels of radioisotopes in northern Europe is likely related to a nuclear reactor that is either operating or undergoing maintenance, when very low radioactive releases can occur."
Countries in the region that have reactors, including Russia, have so far denied that the radioactivity was linked to their territories.
The slightly elevated levels of Caesium and Ruthenium "were very low and posed no risk to human health and the environment," the nuclear agency said.
The IAEA said that such emissions can occur as reactors are operating or undergoing maintenance.
Estonia, Finland and Sweden had detected the particles last week. They also reported the detection of some other artificial radionuclides.
The three countries said there had been no events on their territories that could explain the presence of the radionuclides, as did more than 40 other countries that voluntarily provided information to the IAEA.
One or two times a year
Aleksi Mattila, laboratory head with the Finnish Radiation and Nuclear Safety Authority (STUK), also said that such emissions could be a result of normal power plant operations.
"We have these types of detections, typically one or two times a year, so this current case is not anything out of the ordinary," he told.
The international nuclear test-ban treaty body CTBTO in Vienna has also tracked how the emissions have moved across northern Europe and has drawn up a map of an area spanning multiple countries where the radioactivity could have originated.
Neither the IAEA nor the CTBTO have powers to investigate such incidents on the ground, as nuclear safety is a national matter under international nuclear law.