North Korea has been negotiating over its nuclear program with the United States , Russia , China , Japan and South Korea in six-party talks . Satellite spies `` vehicle activity '' at a ballistic missile site , U.S. officials say . Comment: Joint forces in South Korea elevate surveillance alert in response to North 's threat .
Satellite spies `` vehicle activity '' at a ballistic missile site , U.S. officials say . Comment: Joint forces in South Korea elevate surveillance alert in response to North 's threat .