Russian security officials have released new details about a group suspected of planning a terror attack in Moscow with support from the Islamic State group, saying it was comprised of 12 Russian citizens, including at least one who had been trained in Syria.

Only three suspects have been identified so far and all are from Chechnya, a predominantly Muslim region in southern Russia where an Islamic insurgency still simmers after two separatist wars.

They appeared Tuesday in a Moscow court, which ordered them held for two months.

Security officials previously had not said how many suspects were arrested following Sunday's raid of a Moscow apartment where explosives were found.

The head of the Federal Security Service said Tuesday one of the 12 suspects, Aslan Baisultanov, had been trained in Syria.