"Spying on a close ally on German soil is completely unacceptable and we are in full solidarity with our British friends," Maas told the media in Berlin on Wednesday, reports the AP and the BBC, among others.
The man was arrested by German police in Potsdam on Tuesday and is now in custody, suspected of handing over documents to the Russian intelligence service for an unknown amount of money, according to federal German prosecutors.
The fact that the person in question is suspected of having worked for Russia is "extremely serious", the German Foreign Minister Heiko Maas emphasized in his statement, and continued:
- We will follow the future investigations of the federal prosecutors very closely.
And if desired, necessary and possible, we will also support them.
The Russian embassy in Berlin did not want to comment on the case on Wednesday, reports AP with reference to Interfax news agency.
The suspect's home and workplace have been searched.