Prosecutors in Chechnya have opened a criminal investigation after finding "catastrophic" levels of radioactivity at a chemical factory in the republic.
Russian forces launched heavy assaults on Grozny in 1999
Investigators say the radiation - in one place reportedly 58,000 times the usual level - poses a danger to people in the region's capital, Grozny.
The case has also raised fears militants could take radioactive waste to use in a so-called "dirty bomb".
The plant has reportedly not been secured since Russia bombed it in 1999.
For years, rebels in Chechnya have been fighting a separatist struggle against Russian forces.
They have been blamed for bomb attacks in Moscow and on Russian airliners, and the deadly sieges at a school in Beslan, North Ossetia, and in a Moscow theatre.
'No safety steps'
Chechen prosecutors say radioactive materials have been improperly stored at the Grozny Chemical Factory, run by the Chechen Oil and Chemical Industry, and that a "catastrophic radioactivity situation" has developed.
"It's a threat to the population because the leadership of the plant is taking no steps whatsoever to remove the radioactive material or isolate access to the plant," prosecutor Valery Kuznetsov said on Friday, according to the Associated Press.
The Russian prosecutor general's office said between 27 and 29 radioactive elements had been identified at the plant, with the cobalt-60 isotope considered particularly dangerous.
Radioactive materials have a variety of uses in the manufacturing industry.
If not disposed of properly, they can pose a serious threat to people nearby.
The radioactive cloud released by the explosion at the Chernobyl nuclear plant in Ukraine in 1986 may be responsible for 4,000 deaths, according to a recent study.
The radioactivity at one storage centre in the Grozny plant is half that recorded at Chernobyl, Rossiya state television said.
Vladimir Slivyak of the Ecodefense environmental group in Moscow urged the Russian government to remove and secure radioactive materials from the plant as a matter of urgency, warning of the dangers of them falling into the hands of "terrorists".
The risk of nuclear material to unsuspecting people was illustrated in 2002, when three woodsmen, coming across cylinders giving off heat in the forest of Georgia, dragged them back to their camp.
They grew seriously ill and received radiation burns from the containers, which were eventually recovered by a specialist UN team.