Russia’s Federal Customs Service found radioactive material in the luggage of a passenger bound for Iran – at Moscow’s Sheremetyevo international airport.

Federal Customs Service made the discovery after the material triggered an alarm in the airport’s radiation control system.

A search of the luggage revealed 18 pieces of radioactive metal packed in individual steel casings.

Federal Customs Service said that tests showed the material was a radioactive isotope which could be obtained only “as a result of a nuclear reactor’s operations”.

Radiation levels in the area were 20 times above normal. An airport customs spokesman said the material had been identified as sodium-22 but gave no other details.

Sodium-22 is a radioactive isotope of sodium that can be used in medical equipment.

The objects sent to a Moscow prosecutor’s office that deals with air and water transport, the service said in a statement. Russian authorities have opened a criminal investigation.