Rome has ordered the expulsion of two Russian officials over an escalating espionage case that Italian Foreign Minister Luigi Di Maio called an "extremely serious incident" between the NATO member state and Russia.
The Kremlin has responded by saying it hopes ties with Italy can be preserved despite the dispute.
Italian police announced earlier on March 31 that they had detained an Italian Navy captain together with a Russian military official on suspicion of spying.
The Italian Foreign Ministry later said it had summoned Russian Ambassador Sergei Razov over the case.
DiMaio then said via Facebook that he had protested to the Russian ambassador and informed him of the "immediate expulsion of two Russian officials involved in this extremely serious incident."
Relations between Russia and NATO member states have been hit by a number of spy scandals in recent years amid heightened tensions between Moscow and the West.
British Foreign Secretary Dominic Raab said London “stands in solidarity with Italy and its actions today, exposing and taking action against Russia’s malign and destabilising activity that is designed to undermine our NATO ally.”
Russia’s embassy in Rome initially confirmed that an employee of its military attache’s office had been detained and that “details of the case are being clarified.”
"Carabinieri intervened during a clandestine meeting between the two, caught immediately after the transfer of a document by the Italian officer in exchange for a sum of money," the police force said in a statement earlier in the day.
Reuters later quoted Russian President Vladimir Putin's office as saying it hoped ties with Italy would remain constructive and positive despite the case.
The Italian newspaper Corriere della Sera reported that the detained Russian official, who had been working at the Russian Embassy, was ordered expelled along with a superior.
The paper noted that the Italian frigate captain would have possessed not only Italian files but also "top secret NATO documents," thus putting at risk not only Italian security but also that of other countries.
Police said the meeting between the Italian frigate captain and the Russian official took place late the previous day.
Both are suspected of "serious crimes tied to spying and state security," according to the police statement.
It initially said the Italian officer was taken into custody, while "the position of the foreign national is still under consideration in relation to his diplomatic status."
Last week, Bulgaria expelled two Russian diplomats for carrying out activities “incompatible” with their diplomatic status, after authorities in the NATO member state busted an espionage group passing military secrets to Russia.
Moscow called the Bulgarian move “groundless.”