Russia's main intelligence agency, the FSB, said on Monday that the cell included four people, two of whom had records in fighting alongside Daesh terrorists in Syria. It said in a statement that one of the suspects was a Russian while the other three were nationals from Central Asian countries but did not elaborate on their identities. The intelligence agency said the four had been working on a major plot to carry out an attack targeting Moscow's transit system and a shop. It added that the suspects had been making improvised explosive devices in a lab outside Moscow. The cell had been directed by two senior militants who fought on the side of the Daesh terrorist group in Syria, the FSB said, adding that they both hailed from the former Soviet Union. There was no mention of the time of the arrests, which took place outside Moscow, ostensibly inside the lab which the FSB had managed to discover. Russia has been hit by a number of high-profile attacks by Daesh since the country became involved in the war on terror in Syria.