Denmark is on alert after unauthorised drone activity over four airports on Wednesday night

Aalborg airport, a major commercial and military hub, was closed for three hours. Police are investigating the seemingly coordinated incident.

Denmark is on alert due to unauthorised drone activity over its airports on Wednesday night and Thursday morning. Aalborg, Esbjerg, Sonderborg and Skrydstrup airports are all affected by what seems to be a coordinated attack.The Aalborg airport, located in northern Denmark and one of the country’s largest, as it is used both for commercial and military flights, was closed, the Danish police announced. The drones left the area after about three hours. The other three airports were not closed.The North Jutland Police released a statement saying they were closely monitoring the situation at Aalborg, but could not indicate the number of drones involved."We cannot yet comment on the purpose of the drones flying in the area, nor can we say anything about who the actor behind is," chief inspector Jesper Bøjgaard Madsen said. "If we get the opportunity, we will take down the drones," he added.Copenhagen and Oslo airports were also targetedTwo days ago, it was the Copenhagen airport that had similar incidents with drones, which raised security concerns about possible Russian involvement.Authorities said the drones at Aalborg followed a similar pattern to the ones that had halted flights at Copenhagen.The drone attack affected the Danish armed forces and was categorised as "the most serious attack yet on Denmark's infrastructure" by the Danish Prime Minister Mette Frederiksen.Authorities in Norway also shut the airspace at Oslo airport for three hours on Monday evening after a drone was seen."The drones that halted flights at Copenhagen airport were part of a pattern of persistent contestation at our borders," said the European Commission President Ursula von der Leyen on Tuesday.Russia’s ambassador to Denmark stated that suspicions of his country's involvement in the incident were ungrounded. Kremlin spokesman Dmitry Peskov also called the allegations "unfounded."Although Norwegian and Danish authorities are working together on the Copenhagen and Oslo incidents, their investigation has not yet established a connection, Norway's Foreign Minister said on Wednesday.Commercial drones are generally not capable of taking off and flying near airports, as these areas are designated as 'no-fly zones' in their GPS software.Europe is on high alertEurope has been on high alert after several NATO members reported airspace violations by Russia.Last week, Estonia and Poland requested consultations with other NATO allies regarding such incursions in separate incidents.Romania, another NATO member, also reported a breach by Russian drones in its airspace.Russia denied violating Estonia's airspace, while it insisted the Polish incursion was not deliberate. However, it did not comment on the Romania incident.After meeting on Tuesday, NATO issued a statement condemning Russia's actions and warned that it would use "all necessary military and non-military tools" to defend itself."Russia bears full responsibility for these actions, which are escalatory, risk miscalculation, and endanger lives. They must stop," the statement said."We are a defensive alliance, yes, but we are not naive, so we see what is happening," NATO's Secretary General Mark Rutte noted.After his speech to the UN, Donald Trump suggested that Nato nations should shoot down Russian planes breaching their airspace.