The vessel had its tracking equipment deactivated, indicating the vessel wished to avoid detection by Danish authorities.

Amid rising Russian aerial incursions in Europe, drone sightings near a Swedish naval base have set off alarm bells. Drones have led to prolonged shutdowns of airports in Denmark and Norway this week.

Intrusions into NATO’s airspace blamed on Russia have reached an unprecedented scale, raising questions about whether the Kremlin is trying to test the alliance’s willingness to respond to a direct attack or divert its attention and resources from the war in Ukraine.

NATO Secretary General Mark Rutte has assured Danish Prime Minister Mette Frederiksen of the alliance's solidarity following drone incidents at Danish airports. The situation is being taken "very seriously,

Denmark said on Thursday it was weighing whether to invoke Article 4 of NATO's founding treaty after drone incursions briefly shut two of its airports and affected military installations in its western Jutland region overnight.

The Kremlin denies it is behind a series of drone incursions at airports in Denmark and across northern Europe this week, but NATO leaders believe otherwise. Security experts say Russian President Vladimir Putin may slowly be expanding his war battlefield beyond Ukraine.

Denmark reported to NATO allies that unspecified "state actors" were responsible for drone incursions that shut two airports, Latvia's foreign minister told Reuters on Thursday, but Danish officials said it was still unclear who was behind the incidents.