Armenia's security services said on Friday they foiled a deal to sell the radioactive isotope strontium-90, the third such case involving a radioactive substance in the country in three years.

"Two residents of Yerevan, Armen Hunanyan and Alfred Bznuni, were arrested while trying to sell a radioactive substance, strontium-90," Armenia's National Security Service said in a statement.

There were no further details available on the quantity of the seized radioactive substance and potential buyers.

The case drew fresh attention to concerns that unsecured nuclear materials around the former Soviet Union could be sold to violent extremists.

Last year four Armenians were arrested for an attempted sale of strontium-90, the highly radioactive isotope of strontium.

In 2010 the Armenian authorities foiled smuggling of enriched uranium into neighbouring Georgia, with the help of an undercover officer posing as a buyer for Islamic radicals.

Georgian police in 2010 also arrested four people for allegedly trying to sell another radioactive substance, cesium-137.

The International Atomic Energy Agency (IAEA) identifies strontium-90 among most significant radioactive sources that emit high levels of radiation and "require particular attention for safety and security reasons."