Two previous rocket launches in 2006 and 2009 were followed weeks or months later by nuclear tests . An analysis of satellite images shows increased activity at North Korea 's nuclear site . The United States and South Korean militaries have been conducting drills in the region for months, but this is the first time they are operating together on a large scale. It says it is responding in self-defense to `` the hostile policy of the U.S. '' G8 leaders have warned North Korea it faces further isolation over its nuclear program .
An analysis of satellite images shows increased activity at North Korea 's nuclear site . The United States and South Korean militaries have been conducting drills in the region for months, but this is the first time they are operating together on a large scale. It says it is responding in self-defense to `` the hostile policy of the U.S. '' G8 leaders have warned North Korea it faces further isolation over its nuclear program .