A photo shows the Kleine Brogel military base on Nov. 2, 2025, in Peer, Belgium. JILL DELSAUX/BELGA MAG/AFP via Getty Images

Belgium's defense minister expressed concern on Monday about a series of unidentified drone flights over the weekend near a military base where U.S. nuclear weapons are stored, saying they seem to be part of a spying operation.

Defense Minister Theo Francken confirmed that drones had flown into the area near the Kleine Brogel air base in northeast Belgium in two phases on Saturday and Sunday night.

The first phase involved "small drones to test the radio frequencies" of Belgian security services, then later came "big drones to destabilize the area and people," Francken told public broadcaster RTBF.

"It resembles a spy operation. By whom, I don't know. I have a few ideas but I'm going to be careful" about speculating, he said. Last month, several drones were spotted above another Belgian military base near the German border. The operators were not identified.

Russia has been blamed for a number of airspace violations, notably in Estonia and Poland, in recent months. But the perpetrators of a series of mysterious drone flights in Denmark and Germany have been harder to pin down.

A late evening drone sighting at Berlin's Brandenburg airport on Friday suspended flights for nearly two hours. It was not clear who was responsible. On Sunday, some flights were delayed at Bremen Airport in Germany after a drone was spotted in the area, but police did not suspect espionage in that case, local media reported.

Francken ruled out that the weekend drone flights in Belgium might have been a prank. He said that the security services' "jammer didn't work because they tested our radio frequency, and they changed frequency. They have their own frequencies. An amateur doesn't know how to do that."

Asked why it wasn't possible to shoot the drones down, Francken said: "When they're over a military base we can shoot the drones down. When it's nearby, we have to be very careful because they can fall on a house, a car, a person. That's completely different."

This can pose legal challenges too. "It's not entirely clear. We have to clarify the legal grounds," he said.

Francken lamented that Belgium "is chasing after the threat" posed by such drone flights. "We should have bought air defense systems five or 10 years ago," that can deal with drones, he said.

A series of mysterious drone overflights have been spotted in the airspace of European Union member countries in recent weeks.

In October, a Belgian official familiar with the matter confirmed to CBS News that drones had been sighted over Elsenborn military base, and said that the number of drones was under investigation. Belgium is a member of the U.S.-led NATO military alliance but the source told CBS News that only Belgian forces are stationed at the Elsenborn base.

Also last month, Germany's Munich Airport shut down twice in less than 24 hours after multiple drone sightings. An airport in Lithuania also later closed for several hours overnight Saturday due to a possible sighting of balloons.

In September, the Danish defense ministry said drones were "observed at several of Danish defense facilities" during an overnight period. Those drone sightings come after several drones were spotted in the Nordic country days earlier, with some of them temporarily shutting down Danish airports.

Drones have also been spotted near military sites in the U.S. this year. The head of NORAD and NORTHCOM — the military commands that defend North America — told Congress earlier this year that some of the mysterious drones seen flying inside the United States may indeed have been spying.

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