The espionage scandal sparked headlines and a diplomatic row with Moscow.

Italy subsequently expelled two Russian officials and Moscow expelled an Italian diplomat in a tit-for-tat move.

Walter Biot, 58, a frigate captain working in the office of the Chief of the Defence Staff, was arrested in Rome in March 2021 after officers tailing him in a car park saw him hand classified documents to a Russian military officer in exchange for 5,000 euros ($5,440).

Friday's sentence, issued behind closed doors by Rome's criminal court, came nearly a year after a military court sentenced Biot to 30 years in prison.

"We have two proceedings in parallel," Biot's lawyer, Roberto de Vita, told AFP.

He said Biot would appeal against Friday's sentence. An appeal against the military court's March 2023 decision is ongoing.

De Vita said he has argued that Biot cannot be judged twice for the same crime, and called the two parallel cases "without precedent".

Italy's highest appeals court will ultimately be called upon to decide which court's ruling is allowed to take precedence, he said.

Military prosecutors -- who had argued that Biot should be handed a life sentence -- said that some of the 19 documents that Biot allegedly photographed with his smartphone were "highly reserved NATO" ones, of which one was "top secret", according to Italian news agency Ansa.

In the criminal case, Biot was charged with espionage, disclosure of national security secrets and corruption.

Following Biot's arrest, his wife told a newspaper he had been "desperate" for money.

"He's not stupid. He's not irresponsible. It's just that he was desperate," Claudia Carbonara told La Corriere della Sera daily.

Carbonara said his salary of 3,000 euros a month was insufficient to support his family of four children -- one with a serious handicap -- and four dogs.

At the time of arrest, police were unable to detain the Russian embassy official who was meeting Biot because of his diplomatic immunity.

But he and another Russian official were promptly expelled from Italy, while Russia expelled an Italian diplomat in Moscow nearly a month later.