Brussels - The NATO allies have approved the start of Operation Eagle Eye, an unarmed airborne surveillance mission to ensure Yugoslavia heeds limits on troops in Kosovo and keeps its heavy weapons in barracks. The high-altitude American U-2 spy plane is already flying surveillance missions over Kosovo. The overflights and verification mission, under the command of the Organisation for Security and Co-operation in Europe, were key concessions by Yugoslav President Slobodan Milosevic in an agreement with the US envoy, Mr Richard Holbrooke.