SEOUL (Reuters) - South Korea said on Saturday that North Korea’s nuclear capability is expanding fast, echoing alarm around the world over the isolated state’s fifth and biggest nuclear test, carried out in defiance of U.N. sanctions.

North Korea conducted the test on Friday and said it had mastered the ability to mount a warhead on a ballistic missile, ratcheting up a threat that rivals and the United Nations have been powerless to contain.

The test showed North Korean leader Kim Jong Un was unwilling to alter course, and that tougher sanctions and pressure were needed to apply “unbearable pain on the North to leave no choice but to change”, South Korean Foreign Minister Yun Byung-se said.

“North Korea’s nuclear capability is growing and speeding to a considerable level, considering the fifth nuclear test was the strongest in scale and the interval has quickened substantially,” Yun told a ministry meeting convened to discuss the test.

The blast, on the 68th anniversary of North Korea’s founding, drew global condemnation.

The United States said it would work with partners to impose new sanctions, and called on China to use its influence - as North Korea’s main ally - to pressure Pyongyang to end its nuclear program.

In Beijing on Saturday, Chinese Vice Foreign Minister Zhang Yesui told North Korea’s ambassador to China, Ji Jae Ryong, that the test was “not conducive to the peace and stability of the Korean peninsula”, China’s Foreign Ministry said.

“China urges North Korea not to take any more actions that could exacerbate tensions, and return as soon as possible to the correct direction of denuclearisation,” Zhang said.

But Russia was skeptical that more sanctions were the answer, while China was silent on the prospect of a new U.N. Security Council resolution, although state media did carry commentaries criticizing the North.

Under 32-year-old leader Kim, North Korea has sped up development of its nuclear and missile programs, despite U.N. sanctions that were tightened in March and have further isolated the impoverished country.

Related Coverage Key China border city brushes off latest North Korea nuclear test

DENUNCIATION

The Security Council denounced North Korea’s decision to carry out the test and said it would begin work immediately on a resolution. The United States, Britain and France pushed for the 15-member body to impose new sanctions.

U.S. President Barack Obama said after speaking by telephone with South Korean President Park Geun-hye and with Japanese Prime Minister Shinzo Abe on Friday that they had agreed to work with the Security Council and other powers to vigorously enforce existing measures and to take “additional significant steps, including new sanctions”.

Russian Foreign Minister Sergei Lavrov said it may take more than additional sanctions to resolve the crisis, suggesting that a Security Council agreement may prove difficult.

“It is too early to bury the six-party talks. We should look for ways that would allow us to resume them,” Lavrov said.

The talks, aimed at ending the North’s nuclear program, involve the United States, Russia, Japan, South Korea, China, and North Korea, but have been defunct since 2008.

U.S. Secretary of State John Kerry said the United States had repeatedly offered talks to North Korea, but Pyongyang had to accept de-nuclearization, which it had refused to do.

“We have made overture after overture to the dictator of North Korea,” he said, adding that he ultimately hoped for an outcome similar to that reached in nuclear talks with Iran.

China said it was resolutely opposed to the test but Foreign Ministry spokeswoman Hua Chunying would not be drawn on whether China would support tougher sanctions.

On Saturday, the Chinese state-run tabloid the Global Times said North Korea was wrong in thinking that building nuclear weapons would provide it with more security or prestige.

A cut-out of North Korean leader Kim Jong Un is set on fire during an anti-North Korea rally in central Seoul, South Korea, September 10, 2016. REUTERS/Kim Hong-Ji

“Owning nuclear weapons won’t ensure North Korea’s political security,” it said in an editorial. “On the contrary, it is poison that is slowly suffocating the country.”

“OUT OF CONTROL”

South Korea’s Park said late on Friday that Kim was “mentally out of control”, blind to all warnings from the world and neighbors as he sought to maintain power. “The patience of the international community has come to the limit,” she said.

North Korea, which calls the South and the United States its main enemies, said its “scientists and technicians carried out a nuclear explosion test for the judgment of the power of a nuclear warhead”, according to its official KCNA news agency.

It said the test proved North Korea was capable of mounting a nuclear warhead on a medium-range ballistic missile, which it last tested on Monday when Obama and other world leaders were gathered in China for a G20 summit.

Pyongyang’s claims of being able to miniaturize a nuclear warhead have never been independently verified.

Its continued testing in defiance of sanctions presents a challenge to Obama in the final months of his presidency and could become a factor in the U.S. presidential election in November, and a headache to be inherited by whoever wins.

North Korea has been testing different types of missiles at an unprecedented rate this year, and the capability to mount a nuclear warhead would be especially worrisome for its neighbors South Korea and Japan.

The Pentagon does not have evidence that North Korea had been able to miniaturize a nuclear weapon, Pentagon spokesman Gary Ross said. But he added: “Given the consequences of getting it wrong, it is prudent for a military planner to plan for the worst.”

Jeffrey Lewis of the California-based Middlebury Institute of International Studies said the highest estimates of seismic magnitude suggested this was North Korea’s most powerful nuclear test so far, at yield of 20 to 30 kilotonnes.

That would make this test larger than the nuclear bomb dropped by the United States on the Japanese city of Hiroshima in World War Two, which had an output of about 15 kilotonnes.

Slideshow (24 Images)

South Korea’s military put the force of the blast at 10 kilotonnes, which would still be the North’s most powerful blast to date.

“The important thing is that, five tests in, they now have a lot of nuclear test experience. They aren’t a backward state any more,” Lewis said.</s>Media playback is unsupported on your device Media caption A North Korean TV presenter reads out the news

North Korea says it has successfully carried out its fifth nuclear test, in continued defiance of UN resolutions.

A 5.3 magnitude tremor had earlier been detected near its nuclear test site.

South Korea believes it is the North's biggest-ever test, raising fears it has made significant nuclear advances.

South Korean President Park Geun-hye called it an act of "self-destruction" showing the "maniacal recklessness" of leader Kim Jong-un. The US warned of "serious consequences".

China's foreign ministry said Beijing was resolutely opposed to the test and urged North Korea to avoid further action that would worsen the situation.

North Korea is banned by the UN from any tests of nuclear or missile technology and has been hit by five sets of UN sanctions since its first test in 2006.

The North said the latest test had been of a "nuclear warhead that has been standardised to be able to be mounted on strategic ballistic rockets".

Estimates of the explosive yield of the latest blast have varied. South Korea's military said it was about 10 kilotonnes, enough to make it the North's "strongest nuclear test ever". Other experts say initial indications suggest 20 kilotonnes or more.

The bomb dropped by the US on Hiroshima in 1945 had a yield of about 15 kilotonnes.

Image copyright AP Image caption South Korea's military said the test appeared to be the North's biggest yet

Ms Park, who is cutting short an overseas visit, said the test was a "grave challenge" to the international community that would "only earn more sanctions and isolation" for North Korea.

"Such provocation will further accelerate its path to self-destruction," she said.

Japan's Prime Minister Shinzo Abe said his country "absolutely cannot condone" any such test and would "protest adamantly" to Pyongyang.

"North Korea's nuclear development is becoming a graver threat to Japan's safety and severely undermines the peace and safety of the region and the international community," he said.

The White House said President Barack Obama had spoken to both Ms Park and Mr Abe after the latest test.

A statement from press secretary Josh Earnest said Mr Obama had "reiterated the unbreakable US commitment to the security of our allies in Asia and around the world".

Analysis: Steve Evans, BBC News, Seoul

What North Korea's opponents can actually do is problematic.

After the fourth test back in January, China agreed to impose tougher UN sanctions. Further and even tougher sanctions are still possible, like blocking the export of fuel oil to North Korea.

That would be a drastic step which might halt the economy and cause serious suffering to ordinary people.

China and the US are increasingly at odds as China asserts itself in East Asia.

China's bottom line is that it does not want the collapse of the regime in Pyongyang if that leads to a chaotic power vacuum, possibly filled by the US and its allies.

"The president indicated he would continue to consult our allies and partners in the days ahead to ensure provocative actions from North Korea are met with serious consequences."

China's foreign ministry said it would lodge a diplomatic protest. Its statement read: "Today, [North Korea] again conducted a nuclear test despite widespread international opposition - the Chinese government firmly opposes the test."

Russian Foreign Minister Sergei Lavrov expressed "serious concern", adding: "UN Security Council resolutions should be strictly complied with."

Yukiya Amano, head of the International Atomic Energy Agency, said the test was "in clear violation of numerous UN Security Council resolutions and in complete disregard of the repeated demands of the international community. It is a deeply troubling and regrettable act".

Long-expected test

The North often uses nationally important dates as an opportunity to show military strength. Friday is its National Day, on which it celebrates the founding of the current regime.

The test was first detected as a 5.3 magnitude earthquake on Friday morning in north-east North Korea, close to its Punggye-ri underground nuclear test site.

Image copyright GeoEye

Both Japan and China are monitoring radiation levels.

The North's last test in January had a yield of about 6-8 kilotonnes. Pyongyang said it was of a hydrogen bomb, which employs nuclear fusion, although many analysts cast doubt on that claim.

The North said its latest test meant that it could now produce "at will, and as many as it wants, a variety of smaller, lighter and diversified nuclear warheads of higher strike power" for use on ballistic rockets.

The North's claims on "miniaturised" nuclear warheads have never been independently confirmed.

In recent months the North has conducted a series of ballistic missile launches - some of which reached Japanese waters - and has unleashed a rising tide of aggressive rhetoric, threatening nuclear attacks on its enemies.

The North has also been angered by a US and South Korean plan to install an anti-missile defence system in the South and by the allies' massive annual joint military exercises, which are still taking place.</s>(The U.S. Geological Survey reported a 5.3-magnitude seismic event in North Korea on Friday, near a nuclear test site in the northeastern part of the county.

The event at 9:30 a.m. local time had a zero depth. Its epicenter was 11 miles (18 km) east-northeast of Sungjibaegam, North Korea, the USGS said.</s>Magnitude of N.Korea seismic event greater than last one - CTBTO agency

VIENNA, Sept 9 (Reuters) - Preliminary data collected by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) in Vienna indicates that the magnitude of the seismic event detected in North Korea on Friday was greater than a previous one in January, the agency's chief said.

CTBTO Executive Secretary Lassina Zerbo told reporters in Vienna that early information indicated a magnitude on Friday of around 5 compared to 4.8 to 4.9 in January.

North Korea said on Friday that it had successfully conducted a nuclear explosion test, its fifth and most powerful atomic test to date. (Reporting by Kirsti Knolle; Editing by Dominic Evans)</s>U.S., European and Chinese agencies reported that the tremor was recorded at 0030 GMT. The U.S. Geological Survey and European agencies measured the tremor at a magnitude of 5.3.

A South Korea government official and the meteorological agency said it was a suspected nuclear test, and Seoul called an emergency meeting of its National Security Council.

"Today at around 9:30 a.m., we detected an artificial earthquake wave at magnitude 5.0 in the area of North Korea's Punggye-ri and we are analyzing whether it is a nuclear test," South Korea's Joint Chiefs of Staff said in a statement, referring to the North's nuclear test site.

The China Earthquake Networks Center also said the tremor was a suspected explosion. China's environment ministry began emergency radiation monitoring along its borders with North Korea in northeast China, state television reported.

Japanese Prime Minister Shinzo Abe said such a nuclear test could not be tolerated. Japan's foreign minister lodged a protest and Tokyo also sent two military jets to begin measuring for radiation.

Jeffrey Lewis of the California-based Middlebury Institute of International Studies said the highest estimates of seismic magnitude suggested this was the most powerful nuclear test conducted by North Korea so far.

He said the seismic magnitude and surface level indicated a blast with a 20- to 30-kilotonne yield. Such a yield would make this test, if confirmed, larger than the nuclear bomb dropped on the Japanese city of Hiroshima in World War Two and potentially bigger than that dropped on Nagasaki soon after.

"That's the largest DPRK test to date, 20-30kt, at least. Not a happy day," Lewis told Reuters, using the North's official title of the Democratic People's Republic of Korea.

"The important thing is that five tests in, they now have a lot of nuclear test experience. They aren't a backwards state any more," he said.

Initial analysis of North Korea's January test estimated a yield of just 6 kiloton.

South Korea's Yonhap news agency reported that the South's military believed the seismic event indicated a blast with a 10-kilotonne yield, still the largest ever conducted by the secretive North.

Kune Y. Suh, a nuclear engineering professor at Seoul National University, said the latest test, if confirmed, appeared to be two to three times larger than earlier tests, with a potential yield of more than 10 kiloton.

"So North Korea can now show off their nuclear capability proudly," Suh said.

Lassina Zerbo, the head of world monitoring agency the Comprehensive Nuclear-Test-Ban Treaty Organization, said the seismic activity registered on Friday was larger than that triggered by the North's test in January.

That test was recorded with a magnitude of 5.1, according to the U.S. Geological Survey.

The White House's National Security Council said it was aware of seismic activity on the Korean Peninsula. "We are monitoring and continuing to assess the situation in close coordination with our regional partners," an NSC statement said.

U.S.-based 38 North, a North Korea monitoring project, said in a note late on Thursday that satellite images showed fresh activity at North Korea's Punggye-ri test site.

Isolated North Korea's fourth nuclear test in January resulted in tough new U.N. sanctions. It has conducted a series of missile tests since then, including of a submarine-launched missile, in defiance of those resolutions.

North Korea has been under U.N. Security Council sanctions since it first tested an atomic device in 2006.</s>Japan to consider more sanctions on North Korea after nuclear test

TOKYO, Sept 9 (Reuters) - Japan's chief government spokesman said on Friday Tokyo will consider further unilateral sanctions against North Korea after the reclusive North conducted what South Korea said was a nuclear test.

South Korean President Park Geun-hye said North Korea had conducted a nuclear test in clear violation of U.N. Security Council resolutions, after a surface-level seismic event with a magnitude of 5.3 was recorded near the North's nuclear test site. (Reporting by Kaori Kaneko; Editing by Chris Gallagher and Paul Tait)</s>North Korea suspected to have conducted fifth nuclear test

SEOUL, Sept 9 (Reuters) - A seismic tremor was recorded in an area around North Korea's known nuclear site on Friday, and was suspected to be the fifth nuclear test by the isolated nation, South Korea's Yonhap news agency said.

U.S., European and Chinese seismological agencies reported that the tremor was recorded at 0030 GMT at surface level.

A South Korean government official said it was a suspected nuclear test, Yonhap reported, and Seoul called for an emergency National Security Council meeting.

The China Earthquake Networks Center said the tremor was a suspected explosion.

Japan's top government spokesman also said there was a high possibility the seismic event indicated that North Korea had conducted a nuclear test and that relevant ministries had been instructed to gather information.

Two months ago, U.S.-based 38 North, a North Korea monitoring project, said satellite images showed a high level of activity at North Korea's nuclear test site, called Punggye-ri.

Speculation has intensified that North Korea may conduct a fifth nuclear test after the United States blacklisted its leader, Kim Jong Un, on July 6 for human rights abuses.

North Korea conducted its fourth nuclear test in January, resulting in tough new U.N. sanctions. It has conducted a series of missile tests this year, including a submarine-launched missile.

The January test was recorded with a magnitude of 5.1, according to the U.S. Geological Survey.

North Korea has been under U.N. Security Council sanctions since it first tested an atomic device in 2006. (Reporting by Seoul bureau; Editing by Raju Gopalakrishnan and Paul Tait)</s>(CNN) [Breaking news update, posted at 1:11 a.m. ET]

North Korea says a nuclear warhead explosion test was conducted in a nuclear research center located at its northern test site, according to a broadcast from North Korea Television, KCTV.

The KCTV presenter said the test showed the nuclear warhead "has been standardized to be able to be mounted on strategic ballistic rockets. "That would enable North Korea to "produce at will and as many as it wants a variety of smaller, lighter and diversified nuclear warheads of higher strike power."

[Previous story, posted at 12:16 a.m. ET]

North Korea conducted a fifth nuclear test Friday, potentially its most powerful yet, South Korean officials said.

South Korea condemned the test, saying it was a clear violation of the United Nations Security Council resolution. President Park Geun-hye called Kim Jong Un's regime "fanatically reckless."

"The only thing that Kim Jong Un regime can gain from the nuclear tests is stronger sanctions from the international community and its isolation. Such provocation will eventually hasten its path to self-destruction," she said in a statement.

The blast had the explosive power of 10 kilotons, almost twice as large as the previous test, said Kim Nam-wook, from South Korea's Meteorological Administration.

By comparison, the nuclear bomb dropped on Hiroshima was 15 kilotons.

"We are currently analyzing whether it was a successful test," a South Korean defense ministry official told CNN.

A US official told CNN that it looked like a nuclear test but confirmation would be dependent on seismic readings, location of the seismic event and whether it can be matched to an underground test site.

Satellite images had shown new activity at the Punggye-ri nuclear test site in recent weeks, according to North Korea monitoring site 38North.

A small number of mining carts could be seen, as well as a new canopy which was designed to hide activity to the site, analysts said.

In January, North Korea claimed it had successfully tested a hydrogen bomb, a move that was condemned by the UN Security Council and led to punitive sanctions on the North Korean regime.

Japanese Prime Minister Shinzo Abe told reporters Friday that if North Korea had conducted another nuclear test it was "absolutely unacceptable."

"We must lodge a strong protest," he said.

Concern has been growing that North Korea is testing weapons at an unprecedented pace this year, said CNN Seoul correspondent Paula Hancocks.

Sanctions, including ones targeting Kim Jong Un personally, have had little effect.

Philip Yun, executive director of Ploughshares Fund, a group that advocates nuclear disarmament, said that North Korea had become "increasingly aggressive."

"The reason is because the international community is not taking it seriously. There's no prospect right now for any talks or negotiations. This will only escalate the situation," he said.

Earlier, the U.S. Geological Survey reported a 5.3 magnitude earthquake in North Korea, but later termed it an explosion. The South Korea Meteorological Administration measured the quake as magnitude 5.0 but said it believed it was artificial.</s>U.S., European and Chinese seismological agencies reported that the tremor was recorded at 0030 GMT at surface level.

A South Korean government official said it was a suspected nuclear test, Yonhap reported, and Seoul called for an emergency National Security Council meeting.

The China Earthquake Networks Center said the tremor was a suspected explosion.

Japan's top government spokesman also said there was a high possibility the seismic event indicated that North Korea had conducted a nuclear test and that relevant ministries had been instructed to gather information.

Two months ago, U.S.-based 38 North, a North Korea monitoring project, said satellite images showed a high level of activity at North Korea's nuclear test site, called Punggye-ri.

Speculation has intensified that North Korea may conduct a fifth nuclear test after the United States blacklisted its leader, Kim Jong Un, on July 6 for human rights abuses.

North Korea conducted its fourth nuclear test in January, resulting in tough new U.N. sanctions. It has conducted a series of missile tests this year, including a submarine-launched missile.

The January test was recorded with a magnitude of 5.1, according to the U.S. Geological Survey.

North Korea has been under U.N. Security Council sanctions since it first tested an atomic device in 2006.</s>SEOUL, South Korea (AP) — The Latest on North Korea's nuclear test (all times local):

China has condemned North Korea's fifth nuclear test, a key denunciation for Pyongyang by its economic lifeline and only major ally.

The Foreign Ministry issued a statement Friday criticizing North Korea for carrying out a test with "disregard" for international objections. The statement said China "resolutely opposes" the test and called on North Korea to stop any behavior that "worsens the situation."

North Korea said Friday that it had detonated a warhead, hours after South Korean officials said they had detected seismic activity near a known nuclear test site.

China has provided cover to North Korea from worldwide denunciations of its nuclear program. But it toughened its line after Pyongyang carried out long-range missile tests earlier this year, restricting exports of jet fuel into the country and banning some mineral imports.

The statement did not indicate whether China would take any immediate action or support new sanctions.

President Barack Obama has been briefed about the report of seismic activity near a nuclear facility in North Korea.

South Korean officials say it was indeed a nuclear test, the fifth by the North.

Obama returned to Washington from a trip to Asia just before 1 a.m. EDT Friday. His press secretary, Josh Earnest, says Obama received the briefing aboard Air Force One from his national security adviser, Susan Rice.

Earnest says Obama also consulted with South Korean President Park Geun-hye and Prime Minister Shinzo Abe of Japan in separate phone calls.

Earnest says Obama reiterated the unbreakable U.S. commitment to the security of America's allies in Asia and around the world. The spokesman says Obama indicated he would continue to consult America's allies and partners in the days ahead "to ensure provocative actions from North Korea are met with serious consequences."

The spokesman for the State Department, John Kirby, says Secretary of State John Kerry has been briefed on the matter and that officials are monitoring and assessing the situation.

North Korea's state TV says Friday's nuclear test "examined and confirmed" specific features of a nuclear warhead designed to be mounted on ballistic missiles. It says there was no radioactive leakage or adverse environmental impact caused by the test.

North Korea says the test shows the country is ready to hit back if provoked by enemies including the United States, and that it will continue its efforts to strengthen the quantity and quality of its nuclear weapons.

North Korea says it has successfully conducted a nuclear explosion test aimed at examining the power of its nuclear warheads.

North Korea's state TV said Friday that the test elevated the country's nuclear arsenal and is part of its response to the international sanctions following its earlier nuclear test and long-range rocket launch in January and February.

North Korea says it will continue to take efforts to strengthen the quantity and quality of its nuclear weapons.

China says the Ministry of Environmental Protection has activated a contingency plan to begin monitoring radiation levels in provinces bordering North Korea, but says radiation levels are normal.

In Japan, meanwhile, two T-4 trainer aircraft took off from Hyakuri Air Base northeast of Tokyo, carrying a special container to collect air samples for analysis of possible radioactive materials.

Tokyo Gov. Yuriko Koike says Japan's capital city is also testing water samples and monitoring radiation levels in the air to examine possible impact from the North Korean nuclear test.

She told reporters: "I will protect the safety of Tokyo residents."

South Korea says North Korea on Friday conducted its fifth atomic test, producing its biggest-ever explosive yield, after monitors detected artificial seismic waves from a quake measuring a magnitude 5.

Japan's Prime Minister Shinzo Abe told reporters Friday that "there is a possibility that North Korea has forced a nuclear test," citing the temblor showing wave patterns from a non-seismic source.

He says: "If North Korea did conduct a nuclear test, it is absolutely not acceptable, and we must lodge a strong protest."

Japan's Foreign Minister Fumio Kishida also confirmed that Japan Meteorological Agency has detected shaking patterns that are not from a naturally occurred earthquake.

The meteorological agency detected a magnitude 5.3 shaking in North Korea, near the country's nulear test facility.

NHK says Japan's Nuclear Regulation Authority is now analyzing radiation levels at monitoring stations nationwide to see if there is any change.

South Korean President Park Geun-hye has strongly condemned North Korea's nuclear test, saying in a statement that it showed the "fanatic recklessness of the Kim Jong Un government as it clings to a nuclear development."

Park's office says she spoke in Laos with President Barack Obama about the test Friday morning, but didn't immediately reveal more details.

Park says South Korea will employ all available measures to put more pressure on North Korea.

A spokesman for the U.S. National Security Council, Ned Price, says Washington is aware of seismic activity on the Korean Peninsula in the vicinity of a known North Korean nuclear test site.

He says: "We are monitoring and continuing to assess the situation in close coordination with our regional partners."

South Korea says North Korea on Friday conducted its fifth atomic test, producing its biggest-ever explosive yield, after monitors detected artificial seismic waves from a quake measuring a magnitude 5.

The U.S. Geological Survey called the seismic activity an "explosion" on its website.
A 5.3 magnitude seismic event recorded in North Korea is confirmed to be the result of a nuclear weapons test.