U.S. military official tells CNN the incident occurred on July 18 . RC-135 Rivet Joint was on electronic eavesdropping mission in international airspace . The plane is a modified version of an older aircraft that has been used for years by the Air Force to monitor enemy air defenses and other activities. The incident was first reported by the Swedish news agency Svenska Dagbladet . U.S. plane evaded encounter by flying into Swedish airspace without permission .
U.S. military official tells CNN the incident occurred on July 18 . RC-135 Rivet Joint was on electronic eavesdropping mission in international airspace . The plane is a modified version of an older aircraft that has been used for years by the Air Force to monitor enemy air defenses and other activities. U.S. plane evaded encounter by flying into Swedish airspace without permission .