German Chancellor Angela Merkel said there was "hard evidence" that she was the target of Russian hackers in what she called "outrageous" spying attempts.
The comments follow reports in the German newspaper Der Spiegel that Russian military intelligence obtained emails from its parliamentary office in 2015.
Germany's intelligence service has repeatedly accused Russian hackers of spying on lawmakers or political leaders. The Bundestag, the lower house of Germany's parliament, also found that its systems were hacked in May 2015.
"I can honestly say that it hurts me: on the one hand, I work every day for a better relationship with Russia, and when you see, on the other hand, that there is such harsh evidence that Russian forces are involved in doing this. , this is an area of tension, "Merkel told lawmakers on Wednesday.
"Of course, we always reserve the right to take action, including against Russia," he warned.
Merkel was asked about data theft from her office in a question and answer session with parliamentarians in parliament.
"I have the impression that they took relatively indiscriminately what they could," she replied.
"I am very happy that the investigations led the federal prosecutor to put a specific person on the wanted list," she said, without giving further details. "I take these things very seriously."
German daily Sueddeutsche Zeitung reported last week that federal prosecutors had issued an arrest warrant against an alleged officer of Russia's military intelligence agency GRU, identified as Dmitriy Badin, who is already being sought by US officials.
German prosecutors did not confirm the report.
Russia has repeatedly denied any involvement in the 2015 hacker attack on the German parliament, calling the accusations unfounded. Likewise, it rejected accusations of Russian meddling in the 2016 US presidential election and alleged cyber attacks on other Western nations and institutions.
Merkel said "distortion of facts" is also part of "Russia's strategy".
The chancellor said that there is every reason to try to maintain a good relationship with Russia, "but that naturally does not make things easier".