Policemen stand outside the metro station where a blast went off in St. Petersburg, Russia, on April 3, 2017. (Xinhua/Irina Motina)

MOSCOW, April 23 (Xinhua) -- The Russian Federal Security Service (FSB) said Tuesday that it had detained nine suspected terrorists in the country's Far East and North Caucasus.

The FSB detained four suspected terrorists in Russia's Far Eastern Primorsky Territory, according to a statement.

The detainees, belonging to the militant terrorist group Jama'at al-Tawhid wal-Jihad (Organization of Monotheism and Jihad), planned robberies of local businessmen with the aim of going to Syria to participate in hostilities there.

During the detention, components for making explosives, a traumatic pistol converted for firing real munitions, religious extremist literature, and Islamic State propaganda materials were seized, the statement said.

The detainees maintained contact with foreign terrorist emissaries, the statement said, without providing more details.

In a separate statement, the FSB said that it had exposed a sleeper cell of the Islamic State extremist group, detaining five people in North Caucasus republics of Dagestan and Chechnya, according to Russian media.

The FSB said the group's members had been preparing crimes of a "terrorist nature" against police officers in the cities of Kaspiysk and Grozny with the help of a drone carrying a bomb.

Components of bombs and weapons have been seized from the detainees, it said.