North Korea confirms it has successfully carried out its third underground nuclear test, a move that has drawn international condemnation.
Pyongyang said the test involved a “miniaturized” device and was carried out in a “perfect manner”.
The confirmation came three hours after seismic activity was detected at North Korea’s nuclear test site.
President Barack Obama called for “swift” and “credible” international action in response.
He said the “provocative” nuclear test did not make North Korea more secure, adding that Washington would remain vigilant and steadfast in its defence commitments to its allies in Asia.
The United Nations had warned of “significant consequences” if Pyongyang went ahead.
UN Secretary General Ban Ki-moon has condemned the test as a “clear and grave violation” of UN resolutions and a “deeply destabilizing” provocation.
The Security Council is to hold an emergency meeting at 14:00 GMT on Tuesday in New York, diplomats say.
North Korea previously conducted nuclear tests in 2006 and 2009. It announced in January that it would conduct a third as a response to UN sanctions that were expanded after its December rocket launch.
Confirmation of the test came in a statement from state-run KCNA news agency.
“It was confirmed that the nuclear test that was carried out at a high level in a safe and perfect manner using a miniaturized and lighter nuclear device with greater explosive force than previously did not pose any negative impact on the surrounding ecological environment,” KCNA said.
North Korea confirms it has successfully carried out its third underground nuclear test, a move that has drawn international condemnation
The claim to have tested a “miniaturized” device is likely to alarm observers. The US and North Korea’s neighbors fear Pyongyang’s ultimate goal is to produce a nuclear device small enough to fit on a long-range missile, something it is not yet believed to have mastered.
In December it put a satellite into space using a three-stage rocket – a move condemned by the UN as a banned test of missile technology.
North Korea said the nuclear test – which comes on the eve of President Barack Obama’s State of the Union address – was to “to protect our national security and sovereignty against the reckless hostility of the United States”.
It is the first such test under new leader Kim Jong-un, who took over the leadership after his father Kim Jong-il died in December 2011.
Activity had been observed at the Punggye-ri nuclear test site for several months.
Seismic activity was then detected by monitoring agencies from several nations at 11:57 a.m. A shallow earthquake with a magnitude of 4.9 was recorded, the US Geological Survey said.
Both South Korea and Japan convened emergency meetings of their national security teams shortly afterwards.
“This is an unacceptable threat to the security of the Korean peninsula and north-east Asia, and a challenge to the whole international community,” South Korea’s presidential national security adviser Chun Young-woo said.
Japanese Prime Minister Shinzo Abe said his government would “consider every possible way to address this issue”.
The US, South Korea and Japan had all warned Pyongyang not to go ahead with the test. China, North Korea’s closest ally and biggest trading partner, had also called for restraint.
North Korea has issued another warning, a day after announcing plans for a third nuclear test.
In a statement, Pyongyang pledged “physical counter-measures” against South Korea if it participated in the UN sanctions regime.
The threat came 24 hours after North Korea said it would proceed with a “high-level” nuclear test in a move aimed at “arch-enemy” the US.
The White House condemned the move, labelling it “needlessly provocative”.
North Korea has conducted two nuclear tests in the past, in 2006 and 2009. It gave no time-frame for its third test.
Its announcement followed the adoption by the UN Security Council of a resolution condemning North Korea’s recent rocket launch and extending sanctions.
North Korea says its rocket launch was for the sole purpose of putting a satellite into orbit; the US and North Korea’s neighbors say it was a test of long-range missile technology banned under UN resolutions.
The second warning in two days came in a statement from the Committee for the Peaceful Reunification of the Fatherland, carried by KCNA news agency.
North Korea pledged physical counter-measures against South Korea if it participated in the UN sanctions regime
“If the puppet group of traitors takes a direct part in the UN <<sanctions>>, the DPRK [North Korea] will take strong physical counter-measures against it,” it said, referring to the South Korean leadership.
“<<Sanctions>> mean a war and a declaration of war against us.”
The UN resolution, passed on Tuesday, expanded existing sanctions against Pyongyang that were imposed after its previous nuclear tests and rocket launches.
Washington has also expanded its own sanctions against North Korea, with targets including a Hong Kong-based trading company and two North Korean bank officials based in Beijing.
On Thursday, it spoke out against a third nuclear test.
“Further provocations would only increase Pyongyang’s isolation, and its continued focus on its nuclear and missile programme is doing nothing to help the North Korean people,” White House spokesman Jay Carney told reporters.
Beijing has called for dialogue, urging all parties to act with restraint and “look at the long-term interest”.
But an editorial in China’s state-run Global Times appeared to hint at exasperation.
“If North Korea engages in further nuclear tests, China will not hesitate to reduce its assistance,” the editorial said.
Both North Korea’s previous nuclear tests followed long-range rocket launches.
The North Korean long-range rocket launched last month was largely made using domestic technology, South Korea says.
December’s launch – condemned by its neighbors as a banned missile test – successfully put North Korea’s first satellite in space.
International sanctions prevent North Korea importing advanced technology.
Correspondents say the discovery it was able to produce the “vast majority” of the parts without foreign help will be a cause for concern.
North Korea says the rocket carried a communications satellite into space, but the US and North Korea’s neighbors have long believed such operations represent attempts by Pyongyang to develop long-range missiles.
South Korean military and space experts salvaged 10 pieces of the rocket which it shed into the sea as it took off, including its first-stage engine, and its fuel and oxidizer tanks.
South Korean military and space experts salvaged 10 pieces of North Korean rocket which it shed into the sea as it took off, including its first-stage engine, and its fuel and oxidizer tanks
In its report, the South Korean Defence Ministry said: “North Korea is believed to have made a majority of components itself, although it used commercially available products imported from overseas.”
North Korea has conducted two long-range rocket launches since Kim Jong-un came to power in December 2011. The launch in April failed, but December’s attempt was an apparent success.
The US, Japan and South Korea are seeking a response in the UN Security Council, which banned North Korea from missile tests after nuclear tests in 2006 and 2009.
A South Korean diplomat said a draft resolution calling for tougher sanctions was being circulated at the UN, with a vote in the Security Council expected on Tuesday or Wednesday, South Korea’s Yonhap news agency reports.
North Korea appears to be struggling to control Unha-3 satellite it put into orbit last week, a space expert has said.
The Unha-3 satellite was launched on board a long-range rocket on December 12, in defiance of sanctions and international warnings.
Pyongyang says the device, the size of a washing machine, is working and is beaming revolutionary songs to Earth.
But US astronomer Jonathan McDowell says it may be tumbling, and does not yet appear to be transmitting.
“Those two things are most consistent with the satellite being entirely inactive at this point,” he told the New York Times.
The satellite was designed to point towards Earth, but Jonathan McDowell said the light coming from it was repeatedly brightening and dimming, indicating it was not yet operating as intended.
“The preponderance of the evidence suggests that the satellite failed either during the ascent or shortly afterwards,” he said.
He told the Associated Press news agency that the device was still completing its orbits, and whether working or not, would remain in space for years to come.
North Korea appears to be struggling to control Unha-3 satellite it put into orbit last week
Stuart Eves, principal engineer at Surrey Satellite Technology in the UK, said it was too early to say that the satellite was dead.
He stressed that any spacecraft would be unstable immediately after launch, and that North Korea could be trying to rectify the problem.
“Depending on how they plan to stabilize it, they may have a problem,” he said.
“We take typically two or three days to get a satellite stable, and we know what we’re doing – whereas this is the North Koreans’ first try.
“It would be prudent to wait a little longer and monitor the tumble rate to see whether there’s any attempt to stabilize it.”
However, critics said the North Korean government was likely to view the launch as a success because the real purpose was to test rocket technology.
The UN Security Council condemned the launch, saying it violated two UN resolutions banning Pyongyang from missile tests, passed after its nuclear tests in 2006 and 2009
The launch last week was North Korea’s first successful use of a three-stage rocket to put a satellite into orbit – a similar launch in April failed just after take-off.
It appears to mark another step towards North Korea’s ability to field an intercontinental range ballistic missile.
Such a missile could be used to carry nuclear warheads.
The rocket was celebrated extravagantly in North Korea, with a mass rally held in the capital, Pyongyang.
State media credited the country’s new leader, Kim Jong-un, with the success, praising his “endless loyalty, bravery and wisdom”.
Pyongyang has said it will carry out further launches.
The US, South Korea and Japan want UN sanctions to be strengthened.
But China – North Korea’s main ally – says any UN response should be “conducive to peace” and avoid escalating tensions.