Russia's Foreign Ministry says it has officially informed Montenegro that it is expelling one of the country's diplomats in Moscow.
"This measure is a response to the decision of the Montenegrin side, adopted on March 4, this year, to declare a diplomat of the Russian Embassy in Podgorica persona non grata," the Foreign Ministry said in a statement on March 24.
Earlier this month, the Montenegrin Foreign Ministry declared a Russian diplomat persona non grata, noting that the decision had been made at the behest of the national security agency.
That announcement came after media reports in Montenegro alleged that two members of the Russia Foreign Intelligence Service had met in February with a senior official from the ruling pro-Serbian Democratic Front in the city of Danilovgrad.
Relations between Russia and Montenegro have been complicated for years.
In 2014 Montenegro imposed sanctions against Russia, joining European Union members, after Moscow illegally annexed Ukraine's Crimea region.
In 2016, Montenegro accused Russia of sponsoring a failed coup attempt, allegedly designed to stop Montenegro from joining NATO.