BY A STAFF REPORTER: This is the second in three days in Pyongyang and the first time North Korea has launched a ballistic missile since south Korea and the United States began the largest joint military exercise in five years. Washington and Seoul have stepped up defence cooperation in the face of the growing military and nuclear threat from North Korea, which has conducted increasingly provocative banned weapons tests in recent months. "North Korea fired an unidentified ballistic missile into the East Sea," the Joint Chiefs of Staff said in a statement. '