Bulgarian Prime Minister Kiril Petkov speaks during an interview with Reuters in Sofia, Bulgaria, March 7, 2022.
Bulgarian Prime Minister Kiril Petkov speaks during an interview with Reuters in Sofia, Bulgaria, March 7, 2022. Reuters / SPASIYANA SERGIEVA

Bulgaria's outgoing prime minister on Thursday called on Russia to withdraw a diplomatic ultimatum sent after Sofia expelled 70 Russian diplomatic staff which included a threat to close Russia's embassy in the Balkan nation.

Bulgaria, an EU and NATO member, said on Tuesday it was expelling 70 Russian diplomatic staff over espionage concerns and had set a cap on the size of Moscow's representation as tensions between the two once-close countries fractured over Russia's invasion of Ukraine.

The move, announced by the foreign ministry and Kiril Petkov, the outgoing prime minister, was the largest expulsion of Russian diplomats by Sofia in recent years and would more than half the size of Moscow's diplomatic footprint in Bulgaria if it goes ahead.

In a diplomatic note seen by Reuters, the Russian embassy on Thursday told Sofia to reverse the expulsions decision by midday on Friday. If it did not, the embassy said it would ask Moscow to consider ending Russia's physical diplomatic presence in Bulgaria altogether.

Russian Ambassador Eleonora Mitrofanova, who has called the Bulgarian expulsions an "unprecedented hostile step," was not available for comment.

Petkov in a statement urged Russia to keep diplomatic channels between Moscow and Sofia open despite the expulsions which he said would still leave Russia with 43 diplomatic staff versus only 12 for Bulgaria in Moscow.

"We believe in the need for dialogue, for which diplomatic channels are key," Petkov said.

"For this reason, we ask the Embassy of the Russian Federation to withdraw the note submitted today. For the sake of the past and for the sake of the future, we must be able to take steps forward with mutual respect," he said.

Petkov, who last week lost a parliamentary no-confidence vote, has taken has taken an unusually strong stance over Ukraine against Russia for the leader of a country that enjoyed close ties with Moscow during the communist era.

He sacked his defence minister for refusing to describe as a war what Russia calls its "special military operation" against Ukraine. He also backed EU sanctions against Moscow and agreed to Bulgaria repairing damaged Ukrainian military hardware.

The expulsions angered Bulgaria's Socialists, allies in Petkov's outgoing coalition government, who on Wednesday said they would not back a new cabinet led by him, a move that could bring the country closer to holding elections in the autumn.