Russia on April 20 declared two Bulgarian diplomats "personae non gratae" in a tit-for-tat response to Sofia's expulsion of two Russian diplomats last month over suspected espionage.
The announcement, made in a statement by the Russian Foreign Ministry, came shortly after Bulgaria's ambassador to Moscow was summoned to the ministry a month after Sofia expelled the two Russian diplomats.
The Russian Foreign Ministry called the expulsion of its diplomats from Bulgaria "baseless."
The expulsions came in March after prosecutors charged six people, including current and former military intelligence officers, with spying for Russia.
The Bulgarian Foreign Ministry declared two Russian diplomats “personae non gratae” on March 22 because they had carried out activities “incompatible” with their diplomatic status.
At the time, the Russian Embassy called the decision “groundless” and said that Moscow “reserves the right to retaliate.”
Bulgaria has close cultural, historical, and economic ties with Russia, the country's main energy partner. But relations between Sofia and Moscow have been hit by several spy scandals in recent years.
Last week a Bulgarian arms trader was implicated in a major diplomatic row between Prague and Moscow after Czech intelligence linked Russian military agents to a deadly ammunition depot explosion in 2014 that killed two people.
On March 19, Bulgarian authorities in the NATO member state announced they had busted an espionage group passing military secrets to Russia.
Prosecutors said six people, including former and current military intelligence officers, were detained and charged for passing classified information about Bulgaria, NATO, and the EU to the Russian Embassy in Sofia.
The Sofia Military District Court has ordered five of them remanded in custody, while another suspect was released on bail, according to the BTA news agency.
Since October 2019, the EU and NATO member state has expelled five diplomats and employees of the Russian Embassy accused of conducting intelligence work.