Russian security forces have detained at least 55 members of a banned Islamic group, a spokesman for the FSB security service has said.
Security officers also seized 500 grams of plastic explosive, several hand grenades and leaflets for the organisation, Hizb-e Tahrir.
These are terrorists who want to overthrow the existing regime by military means
"These are terrorists who want to overthrow the existing regime by military means," FSB spokesman Sergei Ignatchenko told Russia's NTV television.
The FSB said the suspects were Central Asians living illegally in Russia.
Some reports said as many as 121 people were arrested in the raids, which took place on Friday but were announced only on Monday.
Fifty-five of the people detained at a Moscow factory where they had reportedly been hiding were branded "terrorists" by the FSB.
The FSB named two of the men as Alisher Musayev of Kyrgyzstan - allegedly the leader of the cell - and Akram Dzhalolov of Tajikistan.
The Sunni organisation was founded in the Middle East in the 1950s and spread to Central Asia after the fall of the Soviet Union.
It seeks to build an Islamic state in Central Asia and reportedly has links to the Taleban.
Its members claim the organisation is not violent.
The group was banned as a terrorist organisation in Russia in February.