Georgia has revealed how it intercepted a group of smugglers trying to sell weapons-grade uranium on the black market.
The men, both Armenian, slipped across the border into Georgia at night before being arrested in a sting operation.
Highly-enriched uranium can be used to make nuclear bombs.
Experts say they are worried that more might be being traded in the region, and that it could be intended for terrorists.
Georgian investigators say that back in March, the two Armenians stashed the highly-enriched uranium in a lead-lined cigarette container, concealed it in the night train from the Armenian capital Yerevan to Tbilisi, and made their own way across the border.
Thinking that they were selling the 18g (0.6oz) sample to an Islamist group, they were caught by an undercover officer in Tbilisi and put on trial.
The quantity was small, and would probably not have been enough for a bomb alone - but the men have said that they intended to sell more.
The exact origins of the uranium are unclear.
It is not the first time weapons-grade material has been intercepted in Georgia.
In 2007 a Russian man was arrested for carrying 100g of uranium, in a sting operation involving US agents.
Each seizure is a reminder of how porous the borders of the Caucasus are, in spite of the efforts of the US to secure them - and of the fact that unknown quantities of potentially lethal materials from Soviet times are still at large.