Italian Foreign Minister Luigi Di Maio is seen at a joint press conference with his Russian counterpart Sergey Lavrov (not pictured) after a meeting in Moscow, Russia, on October 14, 2020.

The expulsions followed the arrest Tuesday of an Italian navy captain and the detention of a Russian military officer who is stationed in Rome, both on charges of espionage.

The two men were "caught in flagrante and by surprise" and were arrested right after the Italian navy captain gave classified information to the Russian officer 'in exchange for money,'" the Carabinieri, or Italian paramilitary police, said in a press release.

The Russian officer's position was being evaluated because of his diplomatic status, the press release said.

Di Maio did not name the two people who were being expelled and it was not immediately clear who the second person concerned could be.

The Italian Foreign Ministry has not yet responded to a request for comment from CNN on the identity of the two expelled officials.

The Russian ambassador was summoned to the Foreign Ministry in Rome on Wednesday morning, Di Maio said.

"During the convocation of the Russian Ambassador to Italy at the Foreign Ministry, we let him know about the strong protest of the Italian Government and notified the immediate expulsion of the two Russian officials involved in this extremely grave affair," the minister's Facebook post said.

"I thank our intelligence [services] and all of the state's apparatus that every day work for the security of our country."

According to the Carabinieri, the arrests Tuesday were the result of lengthy intelligence work carried out by the Italian Internal Security Agency, with the support of the Italian Military Chief of Staff. The Carabinieri's special unit ROS, which also deals with terrorism, conducted the operation with the guidance of the Rome prosecutor's office.

Addressing the Senate Foreign Affairs Commission on Wednesday, Di Maio said the necessary action had been taken immediately to deal with "an extremely serious hostile act."

"What happened is unacceptable and there will be consequences, there is no doubt about that," he said. "It is not acceptable that an officer of our navy is paid for NATO information. Therefore, not only our security is at risk, but that of the whole of NATO."

The Russian embassy in Rome confirmed that a military officer in Rome had been detained on March 30.

"A verification of the circumstances of what happened is taking place," an embassy statement said. "For the time being, we believe that it is inappropriate to make comments on what has taken place. In any event, we hope that what happened is not reflected on the bilateral relationship between Russia and Italy."

Kremlin spokesman Dmitry Peskov appeared to downplay the significance of the affair.

"At the moment, we do not have information about the reasons and circumstances of this detention," he said. "But in any case, we hope that the very positive and constructive character of Russian-Italian relations will be preserved."

UK Foreign Secretary Dominic Raab tweeted Wednesday: "The UK 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."