Since Moscow's invasion of Ukraine, Warsaw has frequently accused Russia of carrying out acts of espionage inside its territory.

A NATO member and key Kyiv ally, much Western aid to Ukraine passes through its neighbour Poland.

The two men in the dock were part of a ring of 16 Ukrainian, Belarusian and Russian nationals arrested by Warsaw in March 2023, accused of preparing acts of sabotage and information-gathering for Moscow.

Ukrainian citizen Maksym L., 23, was jailed for six years by the court in the eastern Lublin region, while 30-year-old Belarusian Uladyslau P. was handed 34 months.

Polish law prohibits the publication of their full names.

Both were convicted of espionage and participation in an organised criminal group seeking to undermine Poland's interests.

"This was an organised criminal group... whose objective was to collect intelligence to determine the type and volume of aid transferred to Ukraine," said Judge Miroslaw Brzozowski, Polish news agency PAP reported.

The court ruled that the two men had worked for the spy ring between January and March 2023, motivated by financial gain.

They installed surveillance devices along vital cross-border rail routes used for the transportation of military and humanitarian aid to Kyiv, it added.

The group was also responsible for monitoring major points of passage of Western military aid to Ukraine. These included the northern seaports of Gdynia and Gdansk, and the Jasionka airport and the Rzeszow train station near the Ukrainian border.

They communicated with their backers via the social media network Telegram, said the court.