Moscow (CNN) -- Russian authorities on Friday seized radioactive material from the luggage of a passenger on a flight from Moscow to Tehran, Iran.
The luggage, belonging to an Iranian citizen, contained 18 metal objects packed in individual steel cases, Russia's Federal Customs Service said. The agency said the material, the radioactive isotope Sodium-22, can be obtained in a nuclear reactor.
The news sparked concern that the incident may have been related to Iran's nuclear program, which the International Atomic Energy Agency said in a report last month could be geared to produce weapons. Iran has repeatedly said its nuclear program is solely for peaceful purposes.
Nuclear expert Michael Friedlander said Sodium-22 has no applications related to weapons. It is generally used to calibrate nuclear instruments in medical equipment, he said.
Initial tests showed that radiation levels of the objects were 20 times above normal, the Russian customs service said.
Radiation expert Paddy Regan, a professor at England's University of Surrey, said the material was unlikely to present a major 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, he said.
The customs agency said the objects were sent to a Moscow prosecutor's office that deals with air and water transport.
A criminal investigation is under way.
No details were available on the identity of the Iranian passenger, who apparently flew to Tehran on the flight.
Iranian news media quoted an embassy official in Moscow as saying any reports that the passenger had been arrested were false.
"These false allegations are meant to destroy relations between Iran and Russia," the official told the semi-official Iranian Students News Agency.
"A month ago there was a misunderstanding about a university student who was carrying material used in dentistry," he said. "This misunderstanding was resolved quickly and the student received apologies."
CNN's Jo Shelley, Alla Eshchenko, Danielle Dellorto and Shirzad Bozorgmehr contributed to this report.