The authorities in Georgia have said that two metal boxes seized last month in the capital Tbilisi were filled with radioactive material that could be used to make a "dirty bomb".
Fears of missing nuclear generators in Georgia sparked a huge hunt last year
Georgian officials said the green boxes - found in a taxi during a routine raid near the city's railway station - contained a mixture of substances including Caesium and Strontium.
"These substances could be used to create a so-called 'dirty bomb' which would be operational within a 500 to 600-metre radius, and would create a bigger [area of] radioactive fallout ," Interior Ministry spokesman Givi Mgebriashvili said at a news conference.
According to the Reuters news agency, one of the boxes weighted at least 80kg (170 lbs).
Associated Press said the haul included three curies of Caesium and 12 microcuries of Strontium.
Agencies have described another substance found in the taxi variously as Mustard Gas and a "nerve gas concentrate".
Police suspect the radioactive substances were going to be smuggled into Turkey and sold.
One man was arrested when the taxi was searched on 31 May.
Police say he was intending to take the substances to a relative in the south-western Georgian region of Adzharia, near the Turkish border.
Last year, a team of international experts retrieved two cylinders emitting lethal levels of radiation from a remote forest in the western part of Georgia.
The International Atomic Energy Agency (IAEA) warned after the discovery that there may be other radioactive devices scattered across remote areas of Georgia.
In March this year it called for stricter international security measures to keep such materials out of terrorist hands.
More than 280 radioactive sources have already been recovered from Georgia since the mid-1990s. Some were from abandoned Soviet military bases.
Russia and the United States last year claimed that Al-Qaeda members were taking refuge in Georgia's Pankisi Gorge.