A Russian diesel-electric submarine Krasnodar sails upon its arrival afer taking part in the fight against Islamic State in Syria, in the Black Sea port of Sevastopol, Crimea, August 9, 2017. (REUTERS PHOTO)

MOSCOW, Sept. 29 (Xinhua) -- The Russian Federal Security Service (FSB) said Friday that it has detained two Russians in Crimea on suspicion of spying for Ukraine.

The suspects, a man and a woman, collected and transmitted confidential information about the Russian Black Sea Fleet to Ukrainian special services, an FSB statement said.

The FSB has launched criminal proceedings against them and an investigation is underway. If found guilty of treason, they face imprisonment for up to 20 years.

The autonomous republic of Crimea, formerly part of Ukraine, was absorbed into Russia in March 2014 following a local referendum, which was recognized by Moscow but rejected by Kiev and its allies.

Since then, the FSB has published several reports on the detention of suspected Ukrainian spies or saboteurs in Crimea, but Ukraine has consistently denied such acts.