LONDON — Drone overflights again caused disruptions at Danish airports on Wednesday night, officials said, in the latest instance of unexplained drone sightings over sensitive facilities in the Scandinavian nation.

Danish officials held a press conference on Thursday morning detailing the latest incidents, which prompted the complete closure of Aalborg Airport — which is also used by the Danish armed forces — on the northern tip of Denmark’s Zealand island.

“Drones have been observed near Aalborg Airport and the airspace has been closed,” the Danish National Police said in a statement on Wednesday night. “The police are present and investigating further.”

Danish Justice Minister Peter Hummelgaard said at a Thursday press conference that drones were also reported over the southern cities of Esbjerg and Sonderborg, as well as over the Fighter Wing Skrydstrup air base, which is home to Danish F-16 fighter jets.

“The goal of this kind of hybrid attack is to create fear,” Hummelgaard said. “It is to create discord and it is to make us afraid.”

The Danish government is planning to “acquire new capabilities for detection” and to present a bill that will “provide increased opportunities for infrastructure owners to also shoot down drones,” Hummelgaard added.

The latest reports came after Copenhagen Airport was forced to close for several hours on Monday night, as was Oslo Airport in southern Norway. Both capitals sit along the Skagerrak and Kattegat straits, home to busy shipping lanes which connect the North Sea to the Baltic Sea.

The origin or purpose of the drone flights is not yet clear. But Danish Defense Minister Troels Lund Poulsen told a Thursday press conference, “There can be no doubt that everything points to this being the work of a professional actor when we are talking about such a systematic operation in so many locations at virtually the same time.”

“This is what I would define as a hybrid attack using different types of drones,” Poulsen said, adding that Copenhagen has options to respond through NATO, including by triggering the alliance’s Article 4 which calls for a formal consultation with allies.

“We have no evidence to make the direct link to Russia,” Poulsen added.

Danish Prime Minister Mette Frederiksen said Tuesday that she considered the initial drone intrusions over Copenhagen and elsewhere to be “a serious attack against critical infrastructure in Denmark.”

Asked if Russia — drones from which have repeatedly violated NATO airspace in recent months — should be considered responsible, Frederiksen said, “I cannot reject in any way that it could be Russia.”

The Kremlin on Tuesday dismissed the assertion. “A country that takes a serious position should probably not make such baseless accusations time and time again,” he added.,” Kremlin spokesperson Dmitry Peskov said.

Danish police Chief Superintendent Jens Jespersen told reporters on Tuesday that authorities were investigating several theories as to the origin of the drones, including that they may have been launched from nearby ships.

Danish authorities identified three tankers with links to Russia — the Astrol 1, Pushpa and Oslo Carrier 3 — as possible launch points, Reuters reported.

Of the three, only the Pushpa was close to Aalborg on Wednesday night when the latest drone overflights were reported. 

As of Thursday morning, open-source maritime tracking websites showed the Pushpa sailing southwest through the North Sea toward the English Channel, with its eventual destination listed as Vadinar in India.

The Ukrainian government’s “War Sanctions” website lists the Pushpa as part of Russia’s so-called “shadow fleet” of tankers — vessels that are often uninsured and with unclear ownership which Moscow uses to evade international sanctions.

The Puspha also uses the name Boracay and sails under the flag of Benin, according to the Ukrainian government.

ABC News’ Morgan Winsor and Will Gretsky contributed to this report.