Denmark's Aalborg Airport was closed due to drones in its airspace, the North Jutland Police Department announced on Wednesday night.
"Drones have been observed near Aalborg Airport, and the airspace is closed. The police are present and investigating further," read the official statement.
Earlier, a post by the flight-tracking service FlightRadar noted that three inbound flights to Aalborg had been diverted to other airports.
During a later press conference, the police explained that the initial assessment established that people from Alborg were safe and that the airport wasn't in danger.
They also explained that they couldn't establish where the drones originated from or who was controlling them. "It is too early to say what the goal of the drones is and who is behind it," a police official said. They also noted similarities to reports from earlier this week of drones flying over Copenhagen.
The event also affected Denmark's military forces, as Aalborg serves as a base of operations for the Danish Air Force.
Norwegian and Danish authorities are in close contact regarding the incidents in Copenhagen and Oslo on Monday, but their investigation has not yet established a connection, Norway's Foreign Minister said on Wednesday.
Drones linked with Russia over several European countries
This drone sighting was one of several reported over the last few weeks, with similar events occurring in Estonia and Poland, resulting in actual damage to structures.
On Tuesday, NATO condemned Russia's violation of Estonian airspace, saying the incident was part of a pattern of recent actions that were "escalatory, risk miscalculation, and endanger lives."
"Russia should be in no doubt: NATO and Allies will employ, in accordance with international law, all necessary military and non-military tools to defend ourselves and deter all threats from all directions," the alliance's North Atlantic Council said in a statement.
Estonia said on Friday that three Russian MiG-31 fighter jets had entered Estonian airspace without permission, staying for a total of 12 minutes before they were forced to withdraw in an episode that Western officials said was designed to test NATO's readiness and resolve.
On September 10, Poland shot down drones in its airspace with the backing of military aircraft from its NATO allies, the first time a member of the Western military alliance is known to have fired shots during Russia's war in Ukraine.
Polish Prime Minister Donald Tusk told parliament that it was "the closest we have been to open conflict since World War Two," although he also stated that he had "no reason to believe we're on the brink of war."
Moscow denied responsibility for the incident, with a senior diplomat in Poland saying the drones had come from the direction of Ukraine.