N-Korea has tested most powerful nuclear warhead yet: S-Korea

AP

An international nuclear test monitoring agency said that it had detected an “unusual seismic event” in North Korea, following weeks of speculation that a nuclear test was imminent in the country. Reuters has reported a UNSC diplomat confirming that the quake was a result of a nuclear test in North Korea.
Kim Min-seok, a South Korean Defense Ministry spokesman, also told reporters that North Korea informed China and the United States of its plans to conduct a nuclear test. It was not clear when Pyongyang told Beijing and Washington.
These are the latest developments and reactions:

• North Korea has tested most powerful nuclear warhead yet: South Korea
  
  North Korea is believed to have detonated a nuclear device with a yield of 6-7 kilotons, which is more powerful than bombs used in previous atomic tests, Seoul's defense ministry said Tuesday.
  
  Earlier the USGS upgraded the magnitude of the nuclear tremor in North Korea from 4.9 to 5.1. South Korean, U.S. and Japanese seismic monitoring agencies put the magnitude of Tuesday's quake between 4.9 and 5.2.
  
  Chi Heoncheol, an earthquake specialist quoted by the Associated Press, said a magnitude 3.9 magnitude earthquake and a magnitude 4.5 earthquake were detected in the North's 2006 and 2009 underground nuclear tests.

  by FP Staff 8:58 AM
• 
  Obama promises 'firm action' to North Korea's 'provocative' nuclear test
  
  Full text of US President Barack Obama's statement in response to North Korea's nuclear test:
  
  North Korea announced today that it conducted a third nuclear test. This is a highly provocative act that, following its December 12 ballistic missile launch, undermines regional stability, violates North Korea’s obligations under numerous United Nations Security Council resolutions, contravenes its commitments under the September 19, 2005 Joint Statement of the Six-Party Talks, and increases the risk of proliferation. North Korea’s nuclear weapons and ballistic missile programs constitute a threat to US national security and to international peace and security. The United States remains vigilant in the face of North Korean provocations and steadfast in our defense commitments to allies in the region.
  
  These provocations do not make North Korea more secure. Far from achieving its stated goal of becoming a strong and prosperous nation, North Korea has instead increasingly isolated and impoverished its people through its ill-advised pursuit of weapons of mass destruction and their means of delivery.
  
  The danger posed by North Korea’s threatening activities warrants further swift and credible action by the international community. The United States will also continue to take steps necessary to defend ourselves and our allies. We will strengthen close coordination with allies and partners and work with our Six-Party partners, the United Nations Security Council, and other UN member states to pursue firm action.

  by FP Staff 7:58 AM
• 
  Why this nuclear test could test China's patience as well
  
  North Korea’s nuclear test could bring China’s growing frustration with Pyongyang to a head, reports the Associated Press.
  
  Beijing signaled its unhappiness earlier by agreeing to tightened UN sanctions after North Korea launched a rocket in December, surprising China watchers with its unusually tough line, which prompted harsh criticism from Pyongyang.
  
  And while China isn’t expected to abandon its communist neighbor, it appears to be reassessing ties a year after new North Korean leader Kim Jong Un took office. The question is for how long China, itself under new leader Xi Jinping, will continue to back North Korea’s nettlesomepolicies.