The Foreign Ministry said the diplomats had been declared “persona non grata” and had 72 hours to leave the EU and the NATO member state.
Bulgarian authorities have given two Russian diplomats 72 hours to leave the country for suspected espionage.
Prosecutors said on Friday that six people had been arrested on suspicion of spying on behalf of Russia, including several officials from the European Union’s defense ministry and a NATO member state.
On Monday, they said that “preliminary investigations have shown that two Russian nationals carried out intelligence activities incompatible with diplomatic relations.”
The Foreign Ministry said two Russian diplomats had been “declared persona non grata and had 72 hours to leave the country”.
According to the Bulgarian television channel Nova, the diplomats were officers working for Russian military intelligence.
Prosecutors alleged that those arrested last week belonged to a spy ring led by a former Bulgarian intelligence officer whose wife was acting as an intermediary with the Russian embassy.
The Russian embassy warned in a statement on Facebook that it could respond to the deportations.
He expressed “regret that once again this unfounded action by the Bulgarian authorities does not contribute to a constructive dialogue between Russia and Bulgaria”.
“Russia reserves the right to take retaliatory measures,” he said.
Relations between Bulgaria and Russia have been hit by several spy scandals in recent years.
Between October 2019 and the end of 2020, five Russian diplomats and a technical assistant at the Russian embassy were expelled from Bulgaria.
The disputes deteriorated relations between the two former allies, who had maintained their close cultural, historical and economic ties even after the fall of communism in 1989. Bulgaria was seen as Russia’s closest ally during the Cold War .
The latest case came with EU-Russia relations strained by the poisoning and imprisonment of opposition politician Alexey Navalny and the EU’s decision to sanction senior Russian officials over the affair.
On Monday, Polish Foreign Minister Zbigniew Rau said his country and EU member state “strongly supports our friend and NATO ally Bulgaria in its actions to protect sovereignty from the activities hostile espionage of Russia ”.
Over the weekend, the United States also said it “supports the Bulgarians against these malicious activities on their territory”, while the United Kingdom expressed its full support for “Bulgaria’s efforts to disrupt a network suspected espionage and take action to counter Russia’s hostile actions ”.
NATO Secretary General Jens Stoltenberg told Bulgarian Prime Minister Boyko Borissov by telephone on Monday that the alliance must unite against any malicious activity targeting its member states, the government press office said. Borisov called on Russia to stop spying in the Balkan country.
Fourteen years after joining the EU, Bulgaria is still dependent on Russian energy. With its resorts on the Black Sea, the country is very popular with tourists and Russian owners.