"We regret this unjustified action and expressed that to the Russian government," a German official said in a statement late on Saturday after Der Spiegel magazine reported the German was expelled in retaliation for the Russian's expulsion.
The German diplomat, a woman, worked at the German embassy in Moscow. The Russian diplomat concerned had been under observation by Germany's anti-espionage agency, the Office of the Protection of the Constitution, for several months, Der Spiegel said.
It noted that other comparable cases of diplomats being expelled in the recent past had not led to retaliation.
In July, Germany told the CIA station chief in Berlin to leave the country in response to questions raised about U.S. intelligence activity in Germany, including the discovery of a suspected U.S. spy in the Defense Ministry.
Read more: German Diplomat Expelled From Russia, After Suspected Russian 'Spy' Forced Out Of Bonn