German news magazine Der Spiegel reports that suspicious drone overflights have been detected near the German port city of Kiel and a shipyard where new submarines are being built.
Sources quoted by the magazine said the drones were spotted over Kiel and near the submarine construction facilities of local defence shipbuilder TKMS on Friday, September 26.
This latest incident occurred just four days after drones of still unknown origin were detected flying over the Danish capital Copenhagen, which led to the city's airport being temporarily closed for several hours.
Sources said the overflights near Kiel were conducted using a "mother drone" and smaller drones, which were operating in a seemingly coordinated fashion.
Drone overflights of German maritime and security infrastructure have reportedly been occurring as far back as late August of this year.
In early September, an Estonian-owned cargo ship manned by Russian nationals was boarded and detained by German authorities for suspected espionage following reports that one of the crew had launched a drone and flew it over a German Navy vessel in an undisclosed area on August 26.