The United States on Thursday denounced North Korea for threatening a third nuclear test and imposed new sanctions, in an early showdown for President Barack Obama's second administration.
North Korea, which defiantly put a satellite into orbit last month, had responded furiously to a unanimous vote at the UN Security Council that expanded the number of entities on an international blacklist.
White House spokesman Jay Carney criticized the North Korean statement as "needlessly provocative" and said that a nuclear test "would be a significant violation of United Nations Security Council resolutions."
"Further provocations would only increase Pyongyang's isolation, and its continued focus on its nuclear and missile program is doing nothing to help the North Korean people," Carney told reporters.
Outgoing defense secretary Leon Panetta said that the United States was "fully prepared" for a test from Pyongyang.
"We remain prepared to deal with any kind of provocation from the North Koreans. But I hope... they determine that in the end, it is better to become a part of the international family," Panetta told reporters.
The United States has "no outward indications" that North Korea would carry out a test imminently, he said, but he cautioned that much about the totalitarian state was opaque.
"They have the capability, frankly, to conduct these tests in a way that makes it very difficult to determine whether or not they are doing it," Panetta added.
North Korea says its December 12 launch was a peaceful scientific mission.
Outside experts agree that Pyongyang succeeded in putting a satellite into orbit, but US officials charged that the launch was aimed at developing a ballistic missile that could reach America.
The United States, supported by Japan and South Korea, spearheaded the UN resolution. China, North Korea's main ally, backed the bid after lengthy negotiations in which it agreed to expand the number of entities under existing restrictions rather than create a new set of sanctions.
Undeterred by North Korea's anger, the United States added names to its own blacklist that freezes any US-based assets of designated individuals and groups and makes it a crime for anyone in the United States to assist them.
The State Department blacklisted the Korean Committee for Space Technology, which carries out Pyongyang's rocket launches, and two related individuals.
The Treasury Department imposed sanctions on a Hong Kong-based trading company, Leader (Hong Kong) International Trading Ltd, which it accused of assisting shipments for North Korea's main arms dealer.
It also blacklisted two Beijing-based representatives from the Tanchon Commercial Bank, which it said was the financial arm of Korea's Mining Development Trading Corporation, accused of missile transactions with Iran.
The showdown is deja vu for Obama, who took office in 2009 pledging to reach out to US adversaries but four months later was outraged as North Korea carried out its second nuclear test.
The administration has since held out limited hope for changing North Korean policy. It has described its stance as "strategic patience," with the United States unwilling to make gestures until Pyongyang addresses concerns.
Senator John Kerry, whom Obama named as his next secretary of state, has previously championed engagement with North Korea, including one-on-one talks and food assistance to address reported widespread hunger in the country.
Kerry spoke little about the issue in his confirmation hearing Thursday but said that the United States should speak out "for the prisoners of gulags in North Korea."
Satellite images have indicated that North Korea is pressing ahead with its nuclear program, an emblem of pride and deterrence for Kim Jong-Un's regime.
James Acton, a nuclear expert and physicist at the Carnegie Endowment for International Peace, said that North Korea may want to test with uranium.
"I don't think it's guaranteed that it's uranium, but I think it's probable that it will be a uranium device just to see if they've got that working," he said.
Pyongyang disclosed in November 2010 to visiting US scientists that it was operating a uranium enrichment plant, giving it a second way to build bombs after using plutonium for its two tests.