In October, an unidentified spokesman at the National Defense Commission claimed that the U.S. mainland was within missile range. And at a military parade last April, North Korea showed off what appeared to be an intercontinental ballistic missile.
Satellite photos taken last month at a nuclear test site in Punggye-ri, in far northeast North Korea, showed continued activity that suggested a state of readiness even in winter, according to analysis by 38 North, a North Korea website affiliated with the Johns Hopkins School for Advanced International Studies.
Another nuclear test would bring North Korea a step closer to being able to launch a long-range missile tipped with a nuclear warhead, said Daniel Pinkston, an analyst with the International Crisis Group.
"Their behavior indicates they want to acquire those capabilities," he said. "The ultimate goal is to have a robust nuclear deterrent."