COPENHAGEN, Denmark — Trine, a hotel receptionist in the Danish capital, has had trouble sleeping recently. She is too nervous about the unsettling noise of unidentified drones hovering in the night.

"I live very near the airport, so every night these helicopters and stuff are going around and around," she said, making a whirring sound. "I really need to sleep."

She's not the only one whose nerves were frayed in Denmark.

Danish Prime Minister Mette Frederiksen says a "hybrid war" in Europe is underway, describing it as "the most difficult and dangerous situation since the end of the Second World War."

The government has not officially pinpointed who staged the drone flights, but Prime Minister Frederiksen said: "There is only one country willing to threaten us and it is Russia, and the

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