Danish Prime Minister Mette Frederiksen on Tuesday said the incident at Copenhagen Airport, in which large drones disrupted operations, constituted "the most serious attack on Danish critical infrastructure to date."

"This says something about the times we live in and what we as a society must be prepared for," said Frederiksen, according to the Ritzau news agency.

"Of course, we are not ruling out any possibility as to who is behind it," she added.

Frederiksen noted that the attack aligned with the recent trend "other drone attacks, airspace violations and hacking attacks on European airports."

What happened on Monday?

Copenhagen Airport halted operations on Monday after multiple drones were spotted in the area, Danish police said.

Copenhagen Airport's official X account said it had shut down operations due to "activity."

The airport reopened a few hours later, but recognized there would still be "delays and canceled departures."

Copenhagen police earlier posted on social media that the airport was "closed for take-off and landing, as 2-3 large drones" had been seen "flying in the area."

Police believe 'capable operator' responsible

"We have concluded that this was what we would call a capable operator," Danish police Chief Superintendent Jens Jespersen told reporters on Tuesday.

"It's an actor who has the capabilities, the will and the tools to show off in this way," he said.

The senior police officer said the drones came from several different directions, turning their lights on and off, before disappearing after several hours.

According to the FlightRadar tracking service, around 35 flights were diverted from the airport.

The service said that Copenhagen Airport halted air traffic at 8:26 p.m. local time (1826 UTC).

European Commission President Ursula von der Leyen said that the drones in the Danish capital were "pattern of persistent contestation at our borders."

"Our critical infrastructure is at risk," she wrote on X, adding that all the facts had yet to be established.

Norway also reports drone incident

Meanwhile, a drone incident was reported on the same evening at Oslo Airport in Norway, forcing all traffic to move to one runway, according to Norwegian broadcaster NRK. 

Security concerns in northern Europe have been heightened over a recent spate of Russian sabotage activities, as well as multiple drones and fighter jet incursions into NATO airspace in recent weeks.

Edited by: Saim Dušan Inayatullah, Dmytro Hubenko