A Polish court on Tuesday convicted 14 citizens of Russia, Belarus and Ukraine for preparing acts of sabotage on behalf of Moscow as part of a spy ring.

The defendants were charged last month with acts of espionage such as preparing to derail trains carrying aid to neighbouring Ukraine, and monitoring military facilities and critical infrastructure in the NATO member.

"After examining the case... the court found all the defendants guilty of the crimes charged, and found some of them to be operating within an organised criminal group," judge Jaroslaw Kowalski said while delivering the verdict.

The 14 defendants were convicted in absentia after they all pleaded guilty and skipped the trial.

The members of the spy ring were "Russian, Ukrainian, and Belarusian," Barbara Markowska, spokeswoman for the Lublin court, told AFP.

Two other alleged members of the spy ring will be tried in court separately after they withdrew their initial guilty pleas.

Among those convicted is Maxim S., a Russian ice hockey player for a Polish club from Sosnowiec, whose arrest in June prompted Moscow to express a "strong protest" and demand a "comprehensive explanation" from Poland.

The spy ring also included "two Ukrainian lawyers and a political scientist, a French language teacher, a pharmacy technician, (and) a software engineer," the Rzeczpospolita daily reported.

Investigators said the members of the ring received orders via the Telegram messaging app and were paid in cryptocurrency.

Polish media reported the sums they received ranged from 300 to around 10,000 dollars.

Among the facilities the convicted spies surveilled were the border checkpoints with Ukraine and the major rail routes used to transfer weapons and humanitarian aid to the neighbouring country.

Their tasks also included distributing propaganda handouts inciting hatred towards Ukrainian people.

Poland has been an ardent supporter of Ukraine since Russia launched its full-scale invasion in 2022.