Georgia has arrested three of its nationals and three citizens of Armenia for trying to sell the radioactive substance uranium-238, the ex-Soviet country's security services said Monday.

"They were planning to sell the nuclear material, the uranium (U238) for $200 million in Tbilisi," Georgia's State Security Agency said in a statement.

"They have been detained," the statement said, adding that a court had ruled all six suspects be remanded in pre-trial detention.

The statement said an unspecified amount of the substance was found stored in a container in the home of one of the suspects. The interior ministry declined to provide further details.

If charged and found guilty, the suspects face up to 10 years in prison.

Uranium-238 -- the most common isotope of natural uranium -- cannot undergo nuclear chain-reactions, but can be used for the production of a fissile substance, plutonium-239.

The case highlighted concerns that unsecured nuclear materials across the former Soviet Union could be sold to violent extremists.

Over the past five years, Georgia and Armenia have reported numerous cases of their citizens trying to sell radioactive substances.

In 2012, Armenia foiled a deal to sell radioactive strontium-90. In 2010, Georgia thwarted sale of another radioactive substance, caesium-137.

Also in 2010, Georgian police arrested two Armenian men accused of smuggling 18 grammes (0.6 ounces) of highly enriched uranium from Armenia to Georgia and trying to sell it to an undercover agent posing as an Islamist extremist.