Madrid's international airport was closed for over one hour on Monday due to the reported sighting of drones, authorities in Spain said.
The airport manager, AENA, tweeted that 26 flights had been diverted to other airports by the time air traffic restrictions were lifted at 14.15 p.m. (1315 GMT).
It said that a security committee had been set up to study the incident.
The Transport Ministry announced the closure of the airspace around the Adolfo Surez-Barajas airport in Madrid after Enaire, Spain's air navigation authority, reported the possible presence of drones in the area.
Spain's Civil Guard said an investigation had been opened after two pilots had reported seeing some drones near the airport, which is located just east of the city center.
Enaire, which activated a special procedure to halt landings and takeoffs and diverting flights to other airports, warned in a tweet: A drone is not a toy, it's an aircraft."