A number of European countries have increased vigilance in response to a rise in drone-related incidents.

The pair were arrested on Monday evening after a drone appeared over Oslo’s fortress and opera house in violation of a ban on flying over the centre of the capital.

The incident occurred just a few hours before Oslo and Copenhagen airports shut down for several hours due to drone sightings.

The couple, who police said were Singaporeans in their fifties and sixties, said they were both tourists visiting the Norway.

“Since the two detained individuals are foreign nationals, it will be relevant to initiate a case for deportation or expulsion,” Norwegian prosecutor Andre Kvistad Alme said in an email to AFP.

“The case is at an early stage but at this point we have no reason to suspect that this incident is connected to the drone sightings at Oslo or Copenhagen airports,” Alme said.

“This matter will however be subject to further investigation including interrogations and technical examinations of the drone,” he added.

Some European states experiencing increased drone activity have accused Russia of conducting hybrid operations against countries supporting Ukraine.