Italy has expelled two Russian embassy officials after a Russian military officer and an Italian naval captain were detained for spying, authorities said on Wednesday.
The duo were nabbed on Tuesday during a clandestine meeting in which they attempted to exchange secret documents for money, the Carabinieri forces said in Rome.
The Italian Foreign Ministry said it had summoned Russian Ambassador Sergei Razov regarding the incident and expelled two Russian diplomats.
Foreign Minister Luigi Di Maio described the affair as a "very serious matter" in a Facebook post.
"We express regret over the expulsion of two staff members of the Russian embassy from Rome. We are clarifying the circumstances of taking this decision," the Russian Foreign Ministry said in a statement.
The legal status of the foreigner who was detained - a member of the Russian military with a diplomatic position in Italy - was still being examined, the Carabinieri said.
According to the Italian news agency Ansa, the documents the duo had in possession involved military communications and secret maps.
There have been several incidents of Russian spying in Europe recently.
Bulgaria said this month it had uncovered a group of Bulgarian military members who were allegedly spying for Moscow. Two Russian diplomats were expelled from the country.
Prosecutors in Sweden recently charged a 47-year-old man with espionage for allegedly providing Russia with information about Swedish companies in return for payment.
And in Germany, a man was charged in February after he allegedly passed on floor plans for the Berlin parliament to a Russian intelligence agent.
Identified by the attorney general only as Jens F, the man had worked for a company that repeatedly carried out work on behalf of the Bundestag, the seat of German parliament, inspecting electrical devices used in the building.