A major security breach of French military airspace has been revealed Friday at a moment European officials have been hyping the ‘hybrid warfare’ threat from Russia, which has of late centered on many dozens of ‘mystery’ drone breaches in EU airspace especially near sensitive locations like airports.

French Marines opened fire on five unidentified drones that breached restricted airspace above a key nuclear submarine base Thursday evening, military officials said, according to EuroNews. But one official has said a “jammer” was hot and not necessarily live ammunition. 

At around 7:30pm local at the Île Longue naval base in Brittany, which importantly is the command center for France’s fleet of nuclear-armed ballistic missile submarines, radar detected incoming unauthorized UAVs at the high-secure facility.

The marine infantry battalion responsible for protecting the site immediately deployed anti-drone procedures, which included firing several shots at the aircraft in an effort to disable and bring them down.

As it wasn’t confirmed whether the drones were actually hit, the security forces initiated a large-scale search operation. Authorities still haven’t confirmed that any drones were brought down or recovered.

The drones may have been electronically thwarted or intercepted, based on vague references from French military officials, but not much in the way of details have been offered: 

Defense Minister Catherine Vautrin confirmed that troops at the base intercepted an overflight, without detailing whether they fired shots, used electronic jamming or other means against the aerial intruders. It wasn’t clear who was responsible.

“Any overflight of a military site is prohibited in our country,” Vautrin said. “I want to commend the interception carried out by our military personnel at the Île Longue base.”

The installation is located near Brest in western France, and is guarded by more than 120 maritime forces alongside naval security forces, according to French media.

It hosts four ballistic missile submarines — Le Triomphant, Le Téméraire, Le Vigilant, and Le Terrible — and provides maintenance for the vessels which support the nation’s nuclear deterrent. According to official policy, at least one nuclear submarine is deployed on patrol at all times.

“No link with foreign interference has been established,” Frédéric Teillet, the public prosecutor in Rennes, was quoted in AFP as saying. He also indicated that no operators behind the drones have been apprehended or identified.

European officials have of late and without firm evidence been pointing the finger at Russian intelligence for a series of drone incidents near commercial and military airports and installations in northern Europe.