Deputy Chairman of the State Security Committee Viktor Vegera said the ring comprised four Belarusians and a Russian citizen, who had already surrendered to the Russian Federal Security Service (FSB).
"They were interested in gathering classified information about the missile defenses of the Belarus-Russia Union State, particularly the S-300 air defense systems," Vegera said, adding that their espionage activities had been "fully proven."
A special analytical program aired on Belarus ONT TV channel Sunday showed footage of a confession made by the alleged ringleader, former Belarus officer Vladimir Russkin.
Russkin confessed that he was recruited by Polish intelligence when he was caught at a border checkpoint in an attempt to smuggle alcohol. He later recruited four other officers who had access to classified information.
The spies gathered data on S-300 complexes deployed on combat duty in Belarus and passed the information on computer disks to Polish handlers.
Vegera said criminal cases had been submitted to court, but "no damage was inflicted to the defense capacity of Belarus and Russia."
The defendants may face prison terms from seven to 15 years if convicted, ONT TV said.