North Korea seems `` not as stable as we thought , '' one analyst says . The U.S. and South Korean militaries have been conducting joint exercises in the Yellow Sea for months to practice their ability to counter a possible attack from Pyongyang. Jang Song Thaek was married to Kim 's aunt , was vice chairman of the top military body . North Korea state media say Jang was convicted and executed .
North Korea seems `` not as stable as we thought , '' one analyst says . Some observers warn a provocative move like a missile or nuclear test could follow . Jang Song Thaek was married to Kim 's aunt , was vice chairman of the top military body . North Korea state media say Jang was convicted and executed .