SEOUL, South Korea — North Korea vowed on Thursday to launch more long-range rockets and conduct its third nuclear test, saying that it would build up its capability of striking the United States after the United Nations’s expansion of sanctions against North Korea.
The North’s threat was the boldest challenge its new, untested leader, Kim Jong-un, has posed at his country’s longtime foe, the United States, and its last remaining major ally, China, and rattled governments in Northeast Asia that are undergoing sensitive transitions of power.
In a statement issued through state-run media, the National Defense Commission, the North’s highest governing agency, headed by Mr. Kim, said that “a variety of satellites and long-range rockets which will be launched by the D.P.R.K. one after another and a nuclear test of higher level which will be carried out by it” will be “targeted” at “the U.S., the sworn enemy of the Korean people.”
The statement, which used the acronym for the North’s official name, Democratic People’s Republic of Korea, did not clarify when it would conduct such a test, which would be the first since Mr. Kim came to power after the death of his father, Kim Jong-il, in December 2011.
But citing preparations at the Punggye test site in northeastern North Korea, Army Col. Wi Yong-seob, deputy spokesman of the Defense Ministry of South Korea, said on Thursday, “North Korea can conduct a nuclear test as soon as its leadership makes up its mind.”
North Korea had previously hinted at the possibility of conducting a nuclear test, as its Foreign Ministry did on Wednesday when it issued a scathing statement rejecting a unanimous resolution that the United Nations Security Council adopted on Tuesday. The resolution tightened sanctions and condemned North Korea’s Dec. 12 rocket launching as a violation of earlier resolutions that banned the country from conducting any tests involving ballistic-missile technology.
North Korea has since declared that it would shun any talk on denuclearizing the Korean Peninsula, adding that it would not give up its nuclear weapons until “the denuclearization of the world is realized.”
The North’s statement on Thursday indicated that Mr. Kim, despite recent hints of economic changes and openness in North Korea, was likely to follow the pattern his father established when he ran the country: a cycle of a rocket launching, United Nations condemnation and nuclear testing.
“It’s a major test for Kim Jong-un,” said Koh Yu-hwan, a North Korea specialist at Dongguk University in Seoul. “Unlike the rocket launching in December, which the North has said was conducted because it was his father’s dying wish, a nuclear test will be Kim Jong-un’s decision, one for which he will be held responsible.”
By a “nuclear test of higher level,” North Korea most likely meant that it was seeking the technology of building nuclear warheads small enough to mount on long-range missiles, analysts here said. They said that North Korea could detonate a uranium bomb this time to demonstrate its ability to produce weapons-grade uranium. The North’s two previous nuclear tests, in 2006 and 2009, used some of its limited stockpile of plutonium.
A nuclear test would compel the United States and South Korea to take a tough stance, dispelling hopes that Mr. Kim might use the inaugurations of new government in the countries to open a new path of engagement.
Glyn Davies, Washington’s special envoy on North Korea, warned on Thursday that a nuclear test would be “a mistake and a missed opportunity” for North Korea.
“This is not a moment to increase tensions on the Korean Peninsula,” said Mr. Davies, who was visiting Seoul to coordinate the North Korea policies of President Obama’s second-term administration and the incoming government of President-elect Park Geun-hye in Seoul. From Seoul, Mr. Davies will move on to Beijing and then to Tokyo to continue policy consultations with the new governments there.
President Lee Myung-bak, who will hand over the South Korean presidency to Ms. Park next month, said on Thursday that his “biggest worry” was that North Korea might launch a military provocation in time with the changes of hands in government in Seoul.
On Thursday, the North expressed bitterness at China and Russia’s endorsement of the United Nations resolution, denouncing “those big countries” as “failing to come to their senses.” It said that North Korea’s drive to rebuild its moribund economy and its rocket program, until now billed as a peaceful space project, will now “all orientate toward the purpose of winning in the all-out action for foiling the U.S. and all other hostile forces’ maneuvers.”
“They are making a brigandish assertion that what they launched were satellites but what other country launched was a long-range missile,” the statement said, insisting that North Korea had a sovereign right to test rockets.
Moon Soon-bo, an analyst at the private Sejong Institute, said North Korea’s harsh reaction reflected the pain the isolated regime felt by the new resolution, which expanded the number of ways that countries can interdict and inspect cargo bound for the North.
North Korea said Unha-3 rocket it launched in December put a scientific satellite into orbit. But Washington said the launching was a cover for testing technology for intercontinental ballistic missiles. After analyzing the debris of the rocket North Korea fired in December to put a satellite into orbit, South Korean officials said North Korea indigenously built crucial components of a missile that can fly more than 6,200 miles.
Analysts speculated on Thursday that North Korea might test launch one of its KN-08 missiles. KN-08, first unveiled during a military parade in the North Korean capital, Pyongyang, in April last year, is the North’s biggest missile deployed yet but has never been flight tested, according to officials in Seoul.