Multiple airports in Denmark have been disrupted by drones this week in what its government says is a “hybrid attack” by unknown professional actors, as the country considers whether to invoke NATO’s Article 4 for the first time in its history.

COPENHAGEN (Reuters) -Danish police said on Tuesday that drones that shut the country's main airport on Monday appeared to have been flown by "a capable operator" seeking to demonstrate certain abilities,

Air traffic was suspended at Copenhagen Airport on Monday evening due to reports of drone sightings. Authorities have not ruled out a Russian hybrid attack.View on euronews

All flights in and out of Denmark's Copenhagen Airport were held up for hours after police reported two or three large drones spotted in the vicinity.

Authorities didn't immediately assign blame Tuesday for the two to three large drones that shut Copenhagen Airport.

Large drones that flew over Copenhagen Airport for hours and caused it to shut down were the “most serious attack on Danish critical infrastructure” to date, Prime Minister Mette Frederiksen said on Tuesday.

Sightings of two or three large drones near Copenhagen airport late on Monday halted all take-offs and landings for nearly four hours, as Denmark linked them to a series of suspected Russian drone incursions and other disruptions across Europe.