The drone incursion that stopped flights at Copenhagen airport on Monday night was “the most severe attack on Danish infrastructure so far”, Denmark’s Prime Minister Mette Frederiksen said.

Kastrup airport in Copenhagen was forced to shut for several hours from around 20:30 (18:30 GMT) on Monday following the sighting of a number of drones.

“It says something about the times we live in and what we as a society must be prepared to deal with,” Frederiksen told reporters.

Russian involvement could not be ruled out, Frederiksen added – although Kremlin spokesman Dmitry Peskov called the allegations “unfounded”.

The Danish PM made a link between last night’s events in Denmark and the recent Russian drone incursions in Poland and Romania, as well as the violation of Estonian airspace by Russian fighter jets.

Frederiksen said that the motive for the incursion in Copenhagen had likely been to “disrupt, create unrest… to see how far you can go and test the limits.”

Danish intelligence mirrored this assessment, saying the country was facing a “high threat of sabotage”.

“Someone may not necessarily want to attack us, but rather stress us out and see how we react,” said Flemming Drejer, director of operations at Denmark’s intelligence service PET.

In nearby Norway, Oslo airport too was closed for a period after possible drone sightings.

Around 20,000 passengers were impacted by the closure of Copenhagen airport, which resumed operations after midnight local time.

Earlier on Tuesday Danish police stated they did not know who was behind the drones, but that evidence suggested it was a “capable actor.”

A number of large drones which had come from different directions “quite a long way away” had been observed at Copenhagen airport, said police Inspector Jens Jespersen.

He added the drones, which turned their lights on and off as they approached the airport, had been operated by someone who had the “will and tools to show off… perhaps also to practice.”

Police did not shoot down the drones because the airport is located in a densely built-up area and because there were planes in the air, Insp Jespersen told reporters.

In a post on social media Ukrainian President Volodymyr Zelensky referenced “Russia’s violation” of Nato airspace in Copenhagen on 22 September.

Insp Jespersen refused to comment on Zelensky’s allegations.

“It’s not because I don’t want to, it’s because I simply don’t know,” he said.

The Norwegian Police Security Service said it was working to clarify whether the unconfirmed drone sighting at Oslo airport could be related to the drones observed in Denmark.

Oslo airport was closed between 00:30 and 03:30 and fourteen flights had to be diverted.

Norway’s government said Russia has violated Norwegian airspace three times in 2025 – in April, July and August – adding that it was unclear if this was deliberate or the result of navigation errors.

“Regardless of the cause, this is not acceptable,” Prime Minister Jonas Gahr Store said.

Tensions have been escalating recently after Russian drones and aircraft ventured into central and eastern European airspace, three and a half years after Moscow launched its full-scale invasion of Ukraine.

Earlier in September at least three Russian drones were shot down by Polish and other Nato aircraft in Poland’s airspace. Moscow denied it had been trying to target facilities on Polish soil.

A similar incident occurred in Romania only a few days later when a drone flew into Romanian airspace before disappearing from the radar.

And on Saturday three Russian MiG-31 fighter jets entered Estonian skies and remained there for 12 minutes, leading Nato jets to be scrambled. The incursions were part of a “wider pattern of increasingly irresponsible Russian behaviour,” Nato said in a statement on Tuesday.

In recent days Poland stated it would shoot down any objects that violated its airspace, while Sweden promised to do the same if it spotted any Russian aircraft in its skies.

In response to Russia’s incursions into Poland and Romania, Nato has pledged to move troops and fighter jets eastwards.

Planes from the UK, France, Germany and Denmark are taking part in air defence missions over Poland in a bid to bolster the alliance’s eastern flank.