COPENHAGEN ¨C Copenhagen Airport, the busiest in the Nordic region, said it reopened early on Tuesday after drone sightings halted all takeoffs and landings for nearly four hours, with Norway¡¯s Oslo Airport also reopening after it had shut its airspace over a drone.

Danish police said that the drones that shut the country¡¯s main airport on Monday appeared to have been flown by ¡°a capable operator,¡± adding that no suspects had been identified.

The airports¡¯ shutdown left tens of thousands of passengers stranded as flights were diverted.

¡°We have concluded that this was what we would call a capable operator,¡± Danish police Chief Superintendent Jens Jespersen told reporters on Tuesday, referring to the drones observed in Copenhagen.

¡°It¡¯s an actor who has the capabilities, the will and the tools to show off in this way,¡± Jespersen said, adding that it was too early to say if the incidents in Denmark and Norway were linked.

Copenhagen Airport was closed for four hours when two or three large drones were seen flying in its immediate vicinity, officials said, while the Oslo Airport was closed for three hours following two sightings, according to local police.

Jespersen said the drones in Denmark came from several different directions, turning their lights on and off, before eventually disappearing after several hours.

After it reopened, Copenhagen Airport said on X that delays and some cancelled departures would persist and urged passengers to check with their airlines.

Copenhagen diverted 31 flights to other airports, causing ripple effects that delayed or canceled around 100 flights and affected some 20,000 passengers, a spokesperson told reporters Tuesday.

The airport shutdowns came after a string of disruptions at European airports in recent days.

A cyberattack last Friday knocked out check-in and boarding systems supplied by Collins Aerospace, a unit of RTX, affecting operations at London¡¯s Heathrow and the Berlin and Brussels airports. Over the weekend and into Monday, the fallout continued to snarl travel across the region.

In 2018, drone sightings over the runway at Gatwick Airport near London stranded tens of thousands of passengers and disrupted hundreds of flights at the height of the holiday season.