Drones that halted flights at Denmark's main airport are the most serious attack yet on its critical infrastructure, say police who have linked them to suspected Russian drone incursions and other disruptions across Europe.

Danish Prime Minister Mette Frederiksen said the drone activity seemed designed "to disrupt and create unrest", though authorities refrained from naming suspects.

Sightings of two or three large drones near Copenhagen Airport late on Monday halted all take-offs and landings for nearly four hours.

Authorities in Norway also shut the airspace at Oslo airport for three hours after a drone was seen.

The shutdowns at the Nordic region's busiest airports left tens of thousands of passengers stranded.

"I can't say anything about that. It's not because I don't want to, it'

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