The Italian, a middle-ranking officer serving as a frigate captain, was caught red-handed after a "clandestine meeting" with the Russian late Tuesday in Rome, according to a police statement.

Special operations Carabinieri police swooped in and stopped both men, but only the Italian was arrested.

The Russian, an embassy official, avoided custody thanks to his diplomatic immunity, the statement said.

Police said the suspected spy in the navy was discovered after long investigations led by Italy's domestic intelligence agency AISI, with support from the Chief of the Defence Staff.

Reacting to the arrest, Italy's foreign affairs ministry said it had summoned the Russian ambassador to Rome, Sergey Razov, for urgent talks with the ministry's top civil servant.

The arrest comes against the backdrop of heightened tensions between Moscow and the West, notably over the jailing of Kremlin critic Alexei Navalny, a move which triggered EU sanctions against senior Russian officials.