Moscow - Russia said on Monday that several of its diplomats had been expelled from Poland and that a number of Polish diplomats had left Russia after Moscow took "adequate" measures in return.
It was unclear why the Russian diplomats had been expelled and no more details were immediately available.
"The Polish authorities have taken an unfriendly and unfounded step," said Russia's Foreign Ministry in a statement.
It said: "Russia has undertaken adequate measures in response and a number of Polish diplomats have already Stleft the territory of our country for activities incompatible with their status."
Germany said on Saturday that one of its diplomats had been expelled from Moscow after a Russian diplomat working in Bonn was expelled amid media reports that he was a spy.
Relations between Moscow and European Union member states have been strained by the crisis in Ukraine and by EU sanctions imposed after Russia annexed the Crimea peninsula from Ukraine .