The head of the Swiss army has confirmed that a formation of unidentified drones flew over a military installation.
Benedikt Roos told the SRF public broadcaster that operators reported "not a single drone, but several drones in formation" over their facility.
Roos said sending drone formations over critical infrastructure requires a level of expertise that rules out a teenage prank.
The army has refused to disclose the exact location or timing on security grounds, and has not said whether the pilots have been identified.
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