Slovak authorities have broken a Russian spying network that was operating on Slovak territory, officials said on Tuesday.

Stefan Hamran, the country’s chief police officer said four Slovak nationals have been detained in the case with two of them facing spying and bribery charges.

Prosecutor Daniel Lipsic said the two face up to 13 years in prison if tried and convicted.

“We’re talking about serious cases,” Lipsic said. “It’s about a long term, paid cooperation with the Russian military intelligence service" (known as GRU).

The two are accused of seeking out and gathering highly sensitive, strategic and classified information about Slovakia, its armed forces and NATO and handed them over to undercover GRU officers who were based at the Russian Embassy in the Slovak capital, Bratislava, in exchange for money, Hamran said. He said such a case has not been known in Slovakia before.

Lipsic said the suspects received tens of thousands euros (dollars) from the Russian spies.

“The information the Russian intelligence service was looking for also involved Ukraine,” Lipsic said. He didn’t elaborate at a news conference in Bratislava.

Officers from Slovakia’s National Criminal Agency and the country’s Military Intelligence service joined forces to investigate the case.

Tuesday’s move came a day Slovakia’s Foreign Ministry announced it was expelling three Russian diplomats following its assessment of information from the country’s intelligence services on possible spying and bribery.

The ministry said the diplomats have 72 hours to leave the country. It said their activities violated the Vienna Convention on diplomatic relations.

The ministry said it has also strongly urged the Russian Embassy to make sure the activities of its diplomats were in line with the convention, which both countries are obliged to do.

One of the two charged men was pro-rector and the head of the Security and Defense Department at the Armed Forces Academy in the northern town of Liptovsky Mikulas. The officials identified him as Pavel B., and said he had secret contacts with four GRU officers dating to 2013.

The other one, identified as Bohus G., was working for a leading pro-Russian conspiracy website known as Hlavne spravy. He cooperated with the Russians at least from April 2021 and was using his contacts with a former assistant of a lawmaker in the Slovak Parliament and a former member of the Slovak spy service known as SIS, officials said.

The officials said the two confessed their guilt. The investigation is continuing.