"I can honestly say that it pains me. Everyday I try to build a better relationship with Russia and on the other hand, there is such hard evidence that Russian forces are doing this," the German chancellor told lawmakers.
German Chancellor Angela Merkel has said there is "hard evidence" that she was targeted by Russian hackers in what she called "outrageous" spying attempts.
The comments follow reports in German news outlet Der Spiegel that Russian military intelligence had obtained emails from her parliamentary office in 2015.
Germany's intelligence service has repeatedly accused Russian hackers of spying on lawmakers or leading politicians. The Bundestag, Germany's lower house of parliament, also discovered its systems had been broken into in May 2015.
"I can say honestly that this pains 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 hard evidence that Russian forces are involved in acting this way, this is an area of tension," Merkel told lawmakers on Wednesday.
"Of course we always reserve the right to take measures, including against Russia," she warned.
Merkel was asked about the theft of data from her office in a question-and-answer session with lawmakers in parliament.
"I get the impression that they picked up relatively indiscriminately what they could get," she replied.
"I am very glad that the investigations have now led to the federal prosecutor putting a concrete person on the wanted list,'' she said, without elaborating. "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 with Russia's GRU military intelligence agency identified as Dmitriy Badin, who is already being sought by US authorities.
German prosecutors haven't confirmed the report.
Russia has repeatedly denied any involvement in the 2015 hacking attack on the German parliament, calling the accusations groundless. It has similarly dismissed charges of Russian meddling in the 2016 US presidential election and alleged cyberattacks on other Western nations and institutions.
Merkel said "distortion of facts" was also part of "Russia's strategy".
The Chancellor said there is every reason to try maintaining a good relationship with Russia, "but this naturally doesn't make it easier."