SOFIA (Reuters) - Bulgaria expelled two Russian diplomats who prosecutors suspect were involved in espionage and gave them 48 hours to leave the Balkan country, the foreign ministry said on Friday.

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EU and NATO member Bulgaria, which traditionally keeps close links to Russia, expelled another diplomat over espionage allegations in October and declined to grant a visa to Russia’s incoming defense attache.

The Russian Embassy in Sofia said the two diplomats would leave Bulgaria, but Moscow reserved its right to respond to their expulsions. The embassy said Sofia had handed diplomatic notes to the ambassador without providing any proof that the two had acted in a way incompatible with their status.

Earlier on Friday Foreign Minister Ekaterina Zharieva said the two would most likely be expelled after the foreign ministry was informed about the prosecutors’ allegations.

“We will undertake the action that we are obliged to undertake and will most probably declare them ‘persona non grata’,” she said.

In a separate statement, prosecutors said that a first secretary at the consular section of the Russian embassy had been involved in espionage since 2017, seeking information about the electoral process.

A second diplomat, serving at Russia’s commercial representation office in Sofia, had been collecting information on energy and energy security since October 2018, some of which were state secrets, prosecutors said.

“The decision of the Bulgarian authorities to disseminate this information publicly prior to notifying the Embassy does not correspond to the traditionally constructive spirit of relations between our states,” the Russian embassy said in a posting on its Facebook page.

Bulgaria was Moscow’s most reliable ally in eastern Europe during Soviet times. Despite periodic strains in their post-Soviet ties, however, Russia remains Bulgaria’s biggest energy supplier.

The Balkan country declined to join its NATO and EU allies in expelling Russian diplomats over the poisoning of a former Russian spy, Sergei Skripal, in Britain in 2018.

But on Thursday, prosecutors charged three Russians with the attempted murder of an arms trader and two other Bulgarians whose poisoning is being investigated by Sofia for possible links with the 2018 nerve-agent attack on Skripal.