A Polish citizen, detained by the Polish Internal Security Agency (ABW) on suspicion of spying for Russia, has pleaded guilty to the charge.

“The Internal Security Agency has detained a Polish citizen cooperating with Russia’s special services,” ABW’s spokesman Stanisław Żaryn said on Monday.

“The suspect, who has been passing classified military documents to Russia, has pleaded guilty,” the spokesman added.

“On May 5, ABW agents detained a 43-year-old man on espionage charges,” reads a statement issued by a spokesperson for the minister coordinator of special services.

According to the statement, the materials handed over to Russian special services “have been extremely important for Russian operations on the territory and to the detriment of the Republic of Poland.”

An investigation into the matter is underway.