Unidentified drones have been sighted over sensitive industry locations and the U.S. air base at Ramstein in Germany in recent weeks, the Spiegel news magazine reported on Friday, citing a confidential report by German security authorities.

The report flagged numerous drone sightings made in the evening hours of Dec. 3 and 4 over the air base, according to Spiegel.

A security source told Reuters the report on drone sightings over Ramstein was correct. The German defence ministry declined to comment on the report.

German intelligence chiefs have warned that the country’s support for Ukraine in its war with Russia makes it a target of possible sabotage attempts, with recent security incidents at military barracks raising alarm further.

Spiegel also reported unexplained drone sightings over locations belonging to German arms manufacturer Rheinmetall and chemicals group BASF.

“The safety of BASF sites is our top priority,” a company spokesperson said in an emailed statement. “We therefore keep an eye on suspicious activities at all times and work closely with the relevant security authorities.”

Rheinmetall did not immediately respond to an emailed request for comment.