Airports in Copenhagen and Oslo have reopened this morning, police said, hours after unidentified drones in their airspace caused flight diversions and other travel disruption.
Danish police said that drones that shut the country's main airport appeared to have been flown by "a capable operator", adding that no suspects had been identified.
"It's an actor who has the capabilities, the will and the tools to show off in this way," Danish police Chief Superintendent Jens Jespersen said, adding that it was too early to say if the incidents in Denmark and Norway were linked.
The airports in Copenhagen and Oslo, the two busiest in the Nordic region, were shut for hours after drones were observed in their airspace late yesterday, leaving 20,000 passengers delayed as flights were diverted.
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.
Mr Jespersen said the drones came from several different directions, turning their lights on and off, before eventually disappearing after several hours.
In the Danish capital, police said several large drones seen over the airport for several hours late yesterday eventually flew away on their own.
"The drones have disappeared and the airport is open again," Deputy Police Inspector Jakob Hansen told reporters.
"We didn't take the drones down," he added.
Mr Hansen said police were cooperating with the Danish military and intelligence service to find out where the drones had come from.
He said police were also working with colleagues in Oslo after drone sightings in the Norwegian capital also caused the airport to close for several hours.
"We had two different drone sightings," Oslo airport spokeswoman Monica Fasting said.
"We reopened the airport around 3.15am (2.15am Irish time)," she said.
Flights were diverted to nearby destinations during the closures, and officials at both airports said they expected some delays and disruptions to continue today.
The incidents came after the governments of Poland, Estonia and Romania accused Russia of violating their airspace this month, allegations that Moscow has brushed off.
Asked whether the drones above Copenhagen airport could have come from Russia, Mr Hansen, the deputy police inspector, said: "We don't know at this point."
