Moscow said the German was expelled from Moscow in a retaliatory measure for what it described as an "unfriendly" step earlier by Berlin of expelling a Russian diplomat.
German newsweekly Der Spiegel had reported the expulsion of a German diplomat from Moscow at the weekend, saying it came after Berlin had expelled a Russian diplomat from Russia's consulate-general in Bonn.
The Russian foreign ministry insisted that the incident was unrelated to the fact that German Foreign Minister Frank-Walter Steinmeier is due to visit Moscow tomorrow for talks on Ukraine with his Russian counterpart Sergei Lavrov.
"The Russian side took appropriate measures and a number of Polish diplomats have already left the territory of our country," the ministry said in a statement, without giving any further details.
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It said that it made the move after Poland had earlier expelled Russian diplomats for the same reason, calling this "an unfriendly and absolutely groundless step."
In Brussels, Polish Foreign Minister Grzegorz Schetyna said that Warsaw considered Moscow's move a "symmetric response".
The diplomatic spats came as European Union foreign ministers were set to discuss fresh sanctions against Russia over the conflict in Ukraine.
German Chancellor Angela Merkel accused Russia after attending the G20 summit in Australia of "exporting its influence to destabilise eastern Ukraine" and vowed that the Kremlin would not prevail.
Russia has recently made espionage allegations against citizens of several other nearby NATO member countries, heightening tensions as Moscow finds itself increasingly isolated over its actions in Ukraine.
Russian television reported yesterday that a former member of the Latvian parliament, Aleksejs Holostovs, had been expelled from Russia for spying.