The two men, who were only identified by their initials, K.R. and J.M., pleaded guilty to passing on information to Russia about the Siauliai air base in the centre of the country, which houses NATO's Baltic Air Policing mission, the court said in a statement.

The two men secretly met Russian spies "in Russia or other countries," the statement said.

Court spokesman Vytautas Joncas told the BNS news agency that the two men acted in concert, with one of them responsible for collecting the information, while the other acted as intermediary.

They collaborated over a period of five years.

According to local media reports, one of them was working at the air base at the time of his arrest in December 2017, while the other had taken early retirement.

The trial took place behind closed doors.