Russia on Tuesday sentenced a man in the northern Karelia region to 14 years in prison for state treason, saying he had set fire to railway infrastructure on Ukrainian orders.

Russia has seen sabotage acts on its railways -- which play a key role in Moscow's army supply routes for the Ukraine offensive -- for months, handing out heavy sentences.

A military court sentenced the man in the Karelia region bordering Finland, Russia's Interfax news agency reported Tuesday.

It said the unnamed man last year set fire to railway infrastructure in Karelia's Prionezhsky district.

Russia's FSB security service said it had established there was "contact between this person and his Ukrainian curators", Interfax reported.

As well as state treason, the man was found guilty of helping a terrorist group, making public calls for terrorist acts and cooperating secretly with a foreign state.

Russia regularly hands out heavy sentences to its citizens accused of helping Ukraine.