Sept. 27 (UPI) — Denmark on Saturday reported more suspicious drones flying above its largest military base, the second time its airspace was violated this week after another group of drones grounded commercial flights days ago.

Finland, Germany and Lithuania on Saturday also reported sighting drones in their airspace, which follows reports from other NATO nations, including Estonia, Poland and Romania, that reported airspace violations.

In the latest incident, the BBC reported drones were observed above Karup airbase, forcing the nation’s military base to close airspace to commercial traffic. Drones were spotted flying over the country on Thursday near Skrydstrup air base, causing the closure of Aalborg Airport, as others were detected over the southern cities of Esbjerg and Sonderborg.

Additionally, on Saturday, Lithuania report that three drones were noticed near Vilnius, which delayed several commercial flights, Lithuanian broadcaster LRT reported, while Yle reported that a drone flew over the Valajasosky power plant in Rovaniemi, Finland.

Danish Defense Minister Troels Lund Poulsen has said that there is no evidence directly linking the aircraft to Russia, though there has been a significant rise in Russian violations of allied airspace, according to European leaders.

“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 Thursday after drones were spotted over the country.

In a separate incident, Danish authorities said a Russian warship was spotted near their waters with the tracking system off, the Danish outlet Ekstra Bladet reported.

Kremlin spokesman Dmitry Peskov called the allegations “unfounded.”

The Danish Defense Ministry confirmed that drones appeared near multiple military installations but did not specify which ones, according to the BBC. Denmark’s Defense Command, which did not disclose the number of drones it detected, told the Danish news outlet DR News that it deployed resources in response to the drone incursions.

Karup airbase is home to all of the Danish Armed Forces’ helicopters, airspace surveillance and parts of the Danish Defence Command.

Earlier in the week, on Monday, Denmark’s Copenhagen Airport also halted operations because of drone sightings, as did authorities Norway’s Oslo Airport.

Overnight Wednesday, the airspace above Aalborg Airport in northern Jutland was closed — several flights were cancelled and two inbound flights were diverted for about 1 hour — after police reported a drone, Danish broadcaster TV2 said.

German media also reported drone sightings on Friday night in Schleswig-Holstein, which is near the Danish border.

The incursions over NATO members’ borders have increased in the last few weeks after Poland shot down Russian drones violating its airspace on Sept. 10, which came at the same time as a massive strike on Ukraine at the same time. This was the first time NATO had engaged Russian assets over its territory since Russia’s full-scale invasion of Ukraine in February 2022.

Romania reported a similar violation on Sept. 13 and scrambled F-16s after detecting a Russian drone.

Three Russian MiG-31 jets later entered Estonian airspace over the Gulf of Finland on Sept. 19, which spurred Estonian leaders to invoke Article 4 of the NATO treaty, which allows any member of the alliance to call for consultations if it feels its “territorial integrity, political independence or security” is under threat.