Authorities in Kyrgyzstan say they have arrested two men who were trying to sell a large quantity of plutonium on the black market.
The men were detained last week near the capital, Bishkek, but the news was not immediately released.
There has been growing concern that radioactive materials from former Soviet military or research sites could fall into the hands of extremists.
Plutonium is very toxic and can be used in atomic weapons or as reactor fuel.
The highly radioactive material could be used to make a dirty bomb – a non-nuclear explosive which scatters radioactive material packed inside it.
The national security service in the remote mountainous republic says it arrested two Kyrgyz citizens and confiscated 60 small containers containing plutonium-239.
There is no information on exactly what quantity of plutonium was in the containers.
Kyrgyz security agents tracked the men who were attempting to sell the plutonium and arrested them while posing as buyers.
The origin of the material is unknown.
Security officials say it is not used in Kyrgyzstan, so they think it may have come from one of the neighbouring republics or from Russia.
Earlier this year, another man was arrested in Kyrgyzstan attempting to sell a quantity of caesium-137, another highly radioactive substance.
This came from a Soviet-era military establishment in the south of the country.
There has been growing international concern about the quantities of unguarded or poorly guarded radioactive material left behind in Central Asia by the Soviet military establishment.
Uranium was extensively mined in Kyrgyzstan in Soviet days and there are many sites where radioactive tailings are still stored.
On a number of occasions scrap metal from Kyrgyzstan sold to Chinese companies has been turned back at the border because of its high radioactivity.