The bitter three-year war ended in a truce, not a peace treaty, in 1953, and left the Korean Peninsula divided by the world's most heavily fortified demilitarized zone. The U.S. leads the U.N. Command that governs the truce and stations more than 28,000 troops in ally South Korea, a presence that North Korea cites as a key reason for its drive to build nuclear weapons.
For years, North Korea's neighbors had been negotiating with Pyongyang on providing aid in return for disarmament. North Korea walked away from those talks in 2009 and on Wednesday reiterated that disarmament talks were out of the question.
North Korea is estimated to have stored up enough weaponized plutonium for four to eight bombs, according to scientist Siegfried Hecker, who visited the North's Nyongbyon nuclear complex in 2010.
In 2009, Pyongyang declared that it would begin enriching uranium, which would give North Korea a second way to make atomic weapons.
North Korea carried out underground nuclear tests in 2006 and 2009, both times just weeks after being punished with U.N. sanctions for launching long-range rockets.
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."
Associated Press writers Jean H. Lee and Sam Kim contributed to this report. Follow AP's Korea bureau chief at www.twitter.com/newsjean.
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