BERLIN, Sept. 27 (Xinhua) -- Germany's northern Schleswig-Holstein state has launched an investigation into some unidentified drones that were spotted on Friday night, suspecting their association with espionage or sabotage, the state's interior minister said Saturday.

Sabine Suetterlin-Waack said the state is "closely and continuously" coordinating with the federal government and German armed forces over the matter, but declined to provide details on the number of drones or their flight paths.

Local police have significantly stepped up counter-drone measures and are working closely together with other northern German states, she said.

The Schleswig-Holstein drone sightings came after reports of drone incidents this week in neighboring Denmark, which disrupted air traffic at many airports. Danish Prime Minister Mette Frederiksen has described the drone incursion at the Copenhagen Airport as a "serious attack" on the country's critical infrastructure. ■