Denmark’s Aalborg airport was closed due to drones in its airspace, local police said early on Thursday, two days after the country’s main Copenhagen airport was shut over drone sightings that rattled European aviation.

Danish national police said the drones followed a similar pattern to the ones that had halted flights at Copenhagen airport for four hours a few days earlier. The country’s armed forces were also affected, as Aalborg airport is used as a military base, they added.