Denmark's support for Ukraine, its lack of anti-drone defenses and this week's EU summit in Copenhagen could all explain the unidentified drone sightings over Danish airspace that have been widely blamed on Russia.

Drones have been seen across the Scandinavian country, including over military sites, since Sept. 22, prompting brief closures at several airports and a ban on all civilian drone flights until Friday.

The drone intrusions were "extremely well-executed and also clearly designed to humiliate the authorities, just to show that you can actually fly drones over Danish airports and critical infrastructure," said Rasmus Dahlberg, an expert on hybrid threats.