As part of his preparations for the attack, the suspect was said to have conducted surveillance and acquired bomb-making materials. During a raid on the suspect's home, the FSB said officers seized firearms and means to produce improvised explosive devices.
The news of the thwarted assault comes a year after the FSB thwarted an Islamic State attack on a synagogue in Moscow.
The terror cell, based in Kaluga, 93 miles southwest of the capital, planned to attack worshippers with firearms, the agency said. According to the FSB, the terrorists were members of the Afghan branch of ISIS.
Also in March 2024, an ISIS plot targeting Moscow's Crocus City Hall music venue killed 145 people and wounded 551 others in one of the deadliest terrorist attacks in modern Russian history.