An Italian navy officer has been arrested on suspicion of spying after he was allegedly caught giving classified documents to a Russian military official, authorities say.

The pair - the captain of an Italian frigate and the Russian, who reportedly works at the Russian embassy in Rome - met on Tuesday night.

"Carabinieri intervened during a clandestine meeting between the two, immediately after the transfer of a document by the Italian officer in exchange for a sum of money," Italian police said in a statement.

"Both are accused of serious crimes tied to spying and state security."

The Italian was taken into custody, while the Russian official's position is "under consideration" given his diplomatic status.

According to Italian newspaper Corriere della Sera "classified" documents seized at the Italian's apartment suggest he may have passed on top-secret NATO documents among Italian papers - thereby placing the national security of other countries at risk too.

Italy's foreign ministry summoned the Russian ambassador, Sergei Razov, after the pair were detained by the country's special operations forces.

Foreign Minister Luigi said on Facebook that he had protested firmly to the Russian ambassador and informed him of the "immediate expulsion of two Russian officials involved in this extremely serious matter".

The Russian embassy in Rome confirmed the detention of a diplomat, but would not comment on the incident.

Alexey Fadeev, a spokesperson for the Russian Embassy in Italy, told Sky News: "We confirm the arrest on 30 March in Rome of an official from the office of the Military Attache.

"For now, we consider it inappropriate to comment on the contents of the incident.

"In any case, we hope that what happened is not reflected in the bilateral relations between Russia and Italy."