Russia's customs agency announced Friday it has seized pieces of radioactive metal from the luggage of an Iranian passenger bound for Tehran from one of Moscow's main airports.
It was not immediately clear if the substance could be any use to Iran's controversial nuclear program.
Iran's semi-official news agency ISNA confirmed that material had been seized from the luggage of an Iranian passenger in Moscow about a month ago, but denied it was radioactive.
Russia's Federal Customs Service said in a statement that agents found 18 pieces of metal, packed in steel pencil cases, at Moscow's Sheremetyevo airport after a radiation alert went off. It said the gauges showed that radiation levels were 20 times higher than normal.
Spokeswoman Kseniya Grebenkina told The Associated Press the luggage was seized some time ago, but did not specify when. The Iranian wasn't detained, she said, and it was not clear whether he was still in Russia or not. She did not give his name. The pieces contained Sodium-22, she said, a radioactive isotope of sodium that could be produced in a particle accelerator.
Kelly Classic, a health physicist at the United States' renowned Mayo Clinic, said: "You can't make a nuclear bomb or dirty bomb with it."
"You'd certainly wonder where it came from and why," Classic told The Associated Press. "It's prudent to be a little leery considering where the person's going."
Classic said the isotope can be used in devices that determine the thickness of metals.
Another expert, Michael Unterweger, group leader for the radioactivity group at the U.S. National Institute of Standards and Technology, said it can be used as a calibration source for radiation instrumentation.
Unterweger said "it's really strange" that so much Sodium 22 was in the luggage, but if he were the Russian authorities "I wouldn't worry about it."
Iran's ISNA news agency quoted an official at the Iranian Embassy in Moscow as denying that radioactive materials were seized from the luggage of an Iranian passenger bound for Tehran.
"About a month ago, a misunderstanding arose in connection with (an Iranian) student who was carrying some materials for dentistry uses. The issue was quickly resolved and apologies were offered to him," ISNA quoted the official as saying Friday.
ISNA didn't name the official but quoted him as blaming Western media for publishing incorrect information, although the reports first came from the Russian customs service.
"These reports seek to damage Iran-Russia relations," the official was quoted as saying.
Grebenkina said prosecutors have launched a probe into the incident but insisted that the material seized is not highly radioactive.
It was not immediately clear why the agency chose to make the announcement on Friday. Russia, which built the Bushehr nuclear plant in Iran, has aimed to show the international community that its nuclear cooperation with Iran is not connected to Iran's alleged aim of building nuclear weapons.
The U.S. and Israel have not ruled out a military option against Iran's controversial nuclear program. Iran denies the charge, saying its program is geared toward generating electricity and producing medical radioisotopes to treat cancer patients.
Last month, the U.S. and its Western allies bluntly accused Iran of deceiving the world by trying to hide work on nuclear arms, and the U.N. atomic agency passed a new resolution criticizing Tehran's nuclear defiance.
Sergei Novikov, spokesman for Russia's Rosatom nuclear agency, told the AP that the pieces seized at Moscow airport are highly unlikely to have come from Rosatom and said the isotope is produced by particle accelerators, not by nuclear reactors.
In Russia, universities, research institutes and big medical centers have the technology to produce it, he said.
Novikov said Rosatom has never sold Sodium-22 to Iran, but it has supplied Iran with other types of medical isotopes.
In Washington, State Department spokeswoman Victoria Nuland said officials have contacted Russia for more information, and "Until we hear from the Russians exactly what they've got and how it all went down, I don't think we should evaluate."
A spokesman for the International Atomic Energy Agency, who asked for anonymity because he was not authorized to talk on the subject publicly, said that to his knowledge the agency had not yet been notified by the Russians about the seizure and had no information other than what was being reported by media.
Earlier this year, Atomstroiexport, a Rosatom subsidiary, launched Iran's first nuclear reactor in Bushehr. Russian officials have insisted the deal is in line with international agreements and will oblige Tehran to ship all the spent fuel from the plant back to Russia for reprocessing to avoid a possibility of it being used in a covert weapons program.
The U.S. House of Representatives, meanwhile, endorsed harsher sanctions Wednesday against Iran aimed at derailing its suspected pursuit of nuclear weapons.
Seth Borenstein and Matthew Lee in Washington, Ali Akbar Dareini in Tehran and Jim Heintz in Moscow contributed to this report.