The Russian foreign affairs ministry said on December 5 it has declared a Bulgarian diplomat persona non grata.

Bulgaria’s ambassador to Russia was summoned to the Russian foreign ministry to be handed a note expelling a diplomat, whose name is still unknown, holding a rank equivalent to that of a Russian diplomat expelled from Bulgaria at the end of October.

“This step is a response "mirror" measure to the decision of the Bulgarian authorities to expel from the country in October this year a Russian diplomat,” the ministry said in a note.

At the end of October, Bulgaria expelled one Russian diplomat and refused to issue a visa to an incoming defence attaché at the Russian embassy.

This was the first time Sofia has expelled a Russian diplomat or refused to provide a visa. The country declined to join most European states that expelled diplomats over a nerve agent attack in the UK on former double agent Sergei Skripal and his daughter Yulia in March 2018.

At the time, Sofia said that, although there was a high probability that Russia was behind the attack, it needed more hard evidence in order to expel diplomats.

According to the prosecution in Sofia, the expelled diplomat had held conspiratorial meetings with Bulgarians, including with a senior official with clearance for classified information from the European Union and Nato, since September last year.

In September this year, Bulgaria arrested eight people allegedly involved in espionage for Russia. Of the eight arrested, one has been formally charged, the head of the Russophile National Movement in Bulgaria, Nikolai Malinov.

At the time, the prosecution announced it had discovered data on financial transactions from two international organisations to Malinov and the funds had been used for activities threatening Bulgaria’s national security.

The two organisations are owned by two individuals, Russian businessman Konstantin Malofeev and former KGB general Leonid Reshetnikov. Both were banned from entering Bulgaria for 10 years following the arrests.

As relations between the once friendly states deteriorate, on December 4 Russia’s President Vladimir Putin accused Sofia of intentionally delaying the completion of Turkish Stream pipeline, while praising neighbouring Serbia for almost completing its part.

Russia has decided to build the second leg of Turkish Stream through Bulgaria, Serbia and Hungary. In November, Bulgaria’s Prime Minister Boyko Borissov announced that gas from Turkish Stream will go through Bulgaria and Serbia before May 2020.