Russia’s main domestic security agency says it has arrested four members of the Islamic State group who have been preparing attacks in Moscow.

The Federal Security Service, or FSB, the main KGB successor agency, said the suspects arrested in Moscow Thursday were preparing to strike at the capital’s transport network. The agency said in a statement that the four were working under directions from IS in Syria to prepare attacks using self-made explosive devices.

The FSB said that the suspects were planning to join the IS in Syria after the attack. It didn’t give their names, saying only the group included citizens of Russia and ex-Soviet Central Asian nations.

The arrests follow last month’s suicide bombing in St. Petersburg’s subway that left 16 dead and wounded more than 50.

(AP)