The suspect passed information on military sites and critical infrastructure to Ukrainian intelligence, the agency has said

Russia's Federal Security Service (FSB) says it has detained a North African national in southern Russia on suspicion of spying for Ukrainian military intelligence.

The FSB stated on Tuesday that the man used the Telegram messaging app to stay in touch with an officer from Ukraine's military intelligence agency (HUR). On their instructions, he allegedly collected and sent details of military facilities and critical infrastructure in the southern city of Astrakhan. The agency said the information was exploited by foreign intelligence "to the detriment of Russia's security."

Prosecutors have opened a criminal case on espionage charges, and a court has ordered that the suspect be held in pre-trial detention.

The FSB said Ukrainian intelligence is actively seeking recruits online, using social media and messaging apps including Telegram and WhatsApp to organize attacks inside Russia.

Earlier this week, the agency reported the detention of a 51-year-old woman accused of carrying out a sabotage attack on the Trans-Siberian Railway in Zabaykalsky Region under Ukrainian orders. Investigators said she built an improvised explosive device in August, placed it on the tracks, detonated it, and later sent video proof of the blast to her handler in exchange for payment.

READ MORE: Russian woman detained for sabotage of Trans-Siberian Railway - FSB

On Saturday, a bomb exploded during a railway track inspection in Russia's Orel Region, killing two people and seriously injuring another. In May, a series of explosions destroyed railway bridges in the regions of Bryansk and Kursk. The authorities attributed the incidents to Ukrainian intelligence, saying the attacks left seven dead and more than 100 seriously wounded.