The recorded air concentrations of the particles were very low and posed no risk to human health and the environment, the statement said.
However, the IAEA also said the geographical origin of the release has not yet been determined.
Last week, Estonia, Finland and Sweden reported levels of ruthenium-103, caesium-134 and caesium-137 isotopes in the air which were higher than usual.
The IAEA, in an effort to help identify the possible origin of the radioisotopes, contacted counterparts in Europe and asked for information about whether they were detected in their countries, and if any event there may have been associated with the atmospheric release.
The agency said that by Thursday afternoon, 37 member states* in the European region had voluntarily reported that there were no events on their territories that may have caused the observed radioisotope concentrations.
They also provided information about their own measurements and results. In addition, some countries which have not been approached by the IAEA – Algeria, Canada, Georgia, Japan, Kuwait, Morocco, Qatar, Tajikistan, United Arab Emirates and the US – also reported voluntarily to the IAEA about their measurements and said there were no events on their territories.
The IAEA said that based on its technical analysis of the mix of artificial radionuclides, the release was probably related to a nuclear reactor, either in operation or in maintenance.
The agency said it ruled out the possibilities of the release being related to the improper handling of a radioactive source or being linked to a nuclear fuel processing plant, a spent fuel pool or the use of radiation in industry or medicine.
* The 37 counties are: Albania, Austria, Belgium, Bosnia and Herzegovina, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Netherlands, North Macedonia, Norway, Poland, Portugal, Romania, Russia, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey, Ukraine and the UK.