Drones have flown over Aalborg Airport in northern Denmark, as well as three smaller airports in the country, but it is not immediately clear who was behind the incidents, authorities say.

Defence Minister Troels Lund Poulsen said it appeared a “professional actor” was behind the “systematic” flights, without providing additional details during a news conference on Thursday morning (Thursday afternoon AEST).

Authorities said there was no danger to the public.

The goal of the flyovers was to sow fear and division, Danish Minister of Justice Peter Hummelgaard said on Thursday, adding that the country will seek additional ways to neutralise drones including proposing legislation to allow infrastructure owners to shoot them down.

Flights were halted for several hours at Aalborg Airport, which also serves as a military base. Drone sightings began shortly before 10pm Wednesday and ended just before 1am on Thursday (6am to 9am Thursday AEST).

The airports in Esbjerg, Sønderborg and Skrydstrup also were impacted. Skrydstrup is an air base that is home to some of the Danish military’s fighter jets.

The drones appeared to be flying around the airports with their lights turned on but authorities decided against attempting to shoot down the drones, police said. Additional details were not immediately available.

The Copenhagen drones grounded flights in the Danish capital for hours on Monday night, prompting concerns that Russia could be behind the flyover above Scandinavia’s largest airport.

While it wasn’t immediately clear who was behind the flyover, Denmark’s prime minister and NATO’s secretary-general said that Russian involvement couldn’t be ruled out.

Denmark, already on edge because of its proximity to Russia, will join a group of neighbouring countries on Friday to discuss the European Union’s plans for a “drone wall”.

Russia’s Embassy in Denmark on Thursday rejected claims of Russia’s involvement in the drone incidents.

“It is evident that the incidents involving reported disruptions at Danish airports are a staged provocation,” it said in a statement.

“Undoubtedly, they will be used as a pretext for further escalating tension in the interests of forces seeking by all means to prolong the Ukrainian conflict and extend it to other countries.

“The Russian side firmly rejects the absurd speculations of involvement in the incidents.”

It was not immediately clear whether the Copenhagen flyover was related to the incidents later in the week.