U.S. Air Force monitoring N. Korea with spy plane in S. Korean airspace

미군 정찰기 남한상공 잇따라 출동…대북 감시 비행Following North Korea's warning of military exercises, the U.S. has been carrying out aircraft surveillance to monitor the situation.According to aircraft tracking site 'No callsign', a U.S. Air Force spy plane departed from the U.S. base in Japan on Friday afternoon.The aircraft reportedly flew over South Korean airspace from Friday evening until dawn on Saturday.Another U.S. aircraft also flew over South Korean territory including Seoul on Thursday.Observers say that such actions are to strengthen the monitoring of North Korea following recent provocations.