Germany believes Russia is involved in sabotage at military bases.
The Bundeswehr base in Cologne-Wahn and the NATO airfield in Geilenkirchen are believed to have come under attack.
German military spokesman Ulrich Vonrobert told Bloomberg that a hole had been found in the fence around the Cologne base.
NATO spokesman in Geilenkirchen Donny Demmers said the suspect had attempted to enter the facility but was prevented by security.
Unknown persons apparently tried to contaminate drinking water at military bases.
The official explained that abnormal water quality values indicate an attempt to attack the water supply system.
The investigation will show whether suspicions that Russia was behind it are confirmed, said Markus Faber, chairman of the defence committee of the lower house of parliament in Berlin.
In Germany, the incident that occurred at military bases is considered an intensification of hybrid warfare.
