Two drones were spotted over a military base in western Germany.
This happened a few days after a drone with explosives was found at Leipzig airport, near Ukrainian An-124 "Ruslan" planes, the BBC recalled.
The base is located in the town of Mechernich, in the state of North Rhine-Westphalia, not far from Bonn. Components for the US Patriot air defense systems are stored there.
The press secretary of the Bundeswehr Armed Forces Command said that military police officers were sent to the site, after which the case was transferred to local police.
Some European officials have previously accused Russia of sabotage attempts using drones, but Moscow has called these allegations absurd.
The air defense systems, mainly the Patriots, are crucial to Ukraine's ability to intercept Russian ballistic missiles.
This week, Ukrainian President Volodymyr Zelensky appealed to allies for additional supplies of interceptor missiles.
German Interior Minister Alexander Dobrind told the Bild newspaper on Sunday that Germany had become one of the main targets of "destabilizing attacks".
"We are not in a state of war, but we are becoming a target in a hybrid war every day," said Alexander Dobrind.