Russia has expelled several Polish diplomats in a tit-for-tat response to Poland's expulsion of Russian envoys last month.
The move comes amid heightened tensions as European Union leaders discuss imposing new sanctions against Russia over the ongoing violence in Ukraine.
Polish media reported in mid-October that Russian diplomats had been told to leave Poland "for activities allegedly not compatible with their status".
In response, the Russian Foreign Ministry said in a statement on Monday: ''Unfortunately, the Polish authorities have, indeed, made such an unfriendly and incomprehensible step. In this regard, Russia undertook adequate response measures."
The statement added "several Polish diplomats have left the territory of our country for activities not compatible with their status'' without identifying the number of Polish diplomats expelled.
EU Foreign Affairs chief Federica Mogherini also said in a statement on Monday: ''We will for sure discuss the sanctions, but not only the sanctions - because we all know very well that if we work only on that, but not on the other ... tracks, even sanctions will not work."
EU leaders are also discussing how to react to the November 2 elections by pro-Russians in eastern Ukraine, which the EU has called ''illegal and illegitimate''.
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