Russian authorities seized radioactive material from the luggage of a passenger on a flight from Moscow to Tehran on Friday.
The luggage, belonging to an Iranian citizen, contained 18 metal objects packed in individual steel cases, Russia's Federal Customs Service said in a statement. The agency said the material, the radioactive isotope sodium-22, can be obtained in a nuclear reactor.
Initial tests showed that radiation levels of the objects were 20 times above normal, the customs service said.
The Russian atomic agency Rosatom, however, said sodium-22 is exclusively used for medical and scientific research and does not have a high radiation level. Rosatom contradicted the custom agency's claim that the material can only come from a nuclear reactor.
Radiation expert Paddy Regan, a professor at England's University of Surrey, said the material was unlikely to present a major radiation hazard. He said sodium-22 can be made in medical accelerators and is usually not produced in reactors. It is also not used in reactors as a component of fuel.
The Federal Customs Service said the objects were sent to a Moscow prosecutor's office that deals with air and water transport.
A criminal investigation is under way. The whereabouts of the Iranian passenger was not immediately clear.