Russia’s FSB security service said on Monday it had detained members of what it said was an Islamic State sleeper cell in the Moscow region that had been planning to launch a series of high-profile attacks on the country’s transport system, reported Reuters. 

A video of the detentions showed masked FSB agents detaining men in a residential apartment where they could be seen finding and confiscating grenades, pistols and explosives.

The FSB said in a statement on its website that the detentions had occurred on Sept. 30 and that the cell included Russian citizens from the North Caucasus region who it said were committed to trying to set up a global Islamic caliphate and were directed by foreign militants.

It said the cell had been planning to set off explosives in crowded public places and to target transport infrastructure.

The FSB said it had detained all of the cell’s members, but did not say how many people it had taken into custody. The question of opening criminal cases against them was being decided, it added.

Islamic State, banned in Russia, has threatened to take revenge for Russian air strikes in Syria by shedding blood on Russian soil, and a bomb attack on the St Petersburg metro in April killed 14 people.