Russia has seized radioactive material found in luggage bound for Iran, after radiation levels 20 times higher than the norm were detected in the departure lounge of Sheremetyevo airport in Moscow.
"Tests showed that the Sodium-22 could only have been obtained as the result of the work of a nuclear reactor," the Russian customs agency said in a statement on Friday.
"A criminal inquiry has been opened and the materials transferred to prosecutors."
"Eighteen metallic objects of industrial origin were found, packed into individual steel boxes.
"Tests then found that the objects were in fact the radioactive isotope Sodium-22 that had been machine-produced."
Russia's state nuclear agency Rosatom told the Associated Press that it was unlikely to have been produced in one of its nuclear reactor, and it was more likely to have been made in a particle accelerator in a university or a medical centre. Sodium-22 has medical uses including nuclear imaging.
A spokesperson for the Russian authorities said the discovery had been made some time ago abut would not specify an exact date.