TOKYO, Feb 10 (AFP) - As the Korean nuclear crisis escalates, US spy planes are stepping up activities around the strategic Japanese island of Okinawa, a report said Monday. The only US air force WC-135W plane, which helps collect and identify debris from nuclear weapons detonations, landed at Okinawa's Kadena airbase six days earlier, the Jiji Press news agency quoted informed sources as saying. The aircraft, nicknamed Constant Phoenix and assigned to the Offutt air base in Nebraska, was believed to be still on Okinawa as its departure has not been confirmed. An E-6 Mercury, which provides command and...