The Belgian capital, Brussels, remains on alert after unknown drones flying over the airport and two air force bases caused the cancellation of more than 40 flights on Tuesday.

On Wednesday, Belgian Prime Minister Bart De Wever convened an emergency meeting of the National Security Council on Wednesday.

Interior and Security Minister Bernard Quintin indicated that the situation “requires a national and coordinated approach,” stressing that “the safety of passengers and staff remains the government’s priority,” reported the Belgian news agency Belga.

The police said the devices could not be intercepted, but the National Crisis Centre has been activated to coordinate the response.