MOSCOW (AP) — Russia’s top domestic intelligence agency says it has detained members of a sleeper cell of the Islamic State group and foiled a series of terrorist attacks.

The FSB said in a statement on Monday its operatives on Saturday detained an unspecified number of men outside Moscow. The intelligence agency said the men were from Russia’s majority-Muslim North Caucasus, and reported to IS members based abroad.

The FSB said they were plotting attacks targeting critical infrastructure and public events in Russia, but didn’t give any details. Two improvised explosive devices, grenades and guns were found at their homes.

Similar arrests were reported in August when the FSB said suspects from Central Asia with links to the IS were plotting attacks on civilians in Moscow.