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North Korea's top military body said "the various satellites and long-range rockets that we will fire and the high-level nuclear test we will carry out are targeted at the United States," which it called Pyongyang's "sworn enemy."
The announcement followed UN Security Council approval on Tuesday of a US-backed resolution to censure and sanction North Korea for a rocket launch in December that breached UN rules.
"North Korea's statement is needlessly provocative and a test would be a significant violation of United Nations Security Council resolutions," White House spokesman Jay Carney told reporters. "Further provocations would only increase Pyongyang's isolation."
Carney said Tuesday's Security Council decision "would help impede the growth of weapons of mass destruction programs in North Korea ... and the United States will be making, taking additional steps in that regard."
North Korea is not believed to have the technology to deliver a nuclear warhead capable of hitting the continental United States, although its December launch showed it had the capacity to deliver a rocket that could travel 10,000 km (6,200 miles), potentially putting San Francisco in range, according to an intelligence assessment by South Korea.
Asked whether North Korea's latest threat provided any signs of the direction being taken by its new young leader, leader Kim Jong-un, Carney said: "We judge North Korea by its actions ... We certainly haven't seen a noticeable change in behavior."