Drones have been seen near military facilities including Denmark's largest, following a series of incidents that caused air disruption earlier this week.
The devices were observed above Karup airbase, among others, forcing it to briefly close its airspace to commercial traffic. Possible sightings were also reported in Germany, Norway and Lithuania.
It is the latest in a string of suspicious drone activity in Denmark, raising concerns about the nation's vulnerability to aerial attack and sparking fears of potential Russian involvement.
Danish authorities said Thursday's incursions appeared to be a hybrid attack, but cautioned that they had no evidence to suggest Moscow was behind it.
Friday's incident took place around 20:15 local time and lasted several hours, duty officer Simon Skelsjaer explained. Police are collaborating with the Danish military in their investigation but have not established the origin of the drones, stating they did not shoot them down.
Though civil airspace above the base was briefly closed, it had no impact as no commercial flights were scheduled in the area at the time. The Danish Defence Ministry confirmed that drones were sighted near multiple military installations overnight, but did not specify which ones. The other military installations have not been named by Danish state media.
Some 3,500 people work at Karup airbase, which is home to all of the Danish Armed Forces' helicopters, airspace surveillance, and parts of the Danish Defence Command.
The incursions come just days after drones forced closures at airports that housed military facilities, raising alarm about the nature of these incursions.
Authorities suspect that the drone activity may be part of a broader strategy of indirect aggression from Russia towards NATO member states that are supporting Ukraine. However, the Russian embassy in Copenhagen has denied involvement, calling the speculation absurd.
Danish Prime Minister Mette Frederiksen stated that Russian involvement cannot be ruled out, while authorities perform their due diligence on the incoming data from the ongoing investigations.