South Korea says it has found a small amount of radioactive element from air samples it collected following North Korea's latest nuclear test. If enforced, it would deprive North Korea of 30 percent of its annual fuel imports.
The Chinese say they are implementing sanctions along the border, but they have not been forthcoming in issuing clear restrictions to trading companies, or in reporting how required inspections of all goods crossing the North Korean border are being implemented. That would be much higher than most official estimates, which have varied.
The caving in of land at the site, however, may not have been the result of the estimated 4.9-magnitude quake that took place 8 minutes after the test, the analysts say.
North Korea threatened to use a nuclear weapon against Japan and turn the US into "ashes and darkness" for agreeing on fresh United Nations sanctions this week - rhetoric that is likely to exacerbate tensions in North Asia.
"Japan is no longer needed to exist near us", said the Korea Asia-Pacific Peace Committee, which is North Korea's official propaganda arm. The latest test was said to have been a hydrogen bomb created to be mounted on a newly developed intercontinental ballistic missile that has "great destructive power", state media said following the announcement of the test.
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North Korea's announcement came just hours after a large natural disaster was detected near the country's only known nuclear test site in the mountainous region of North Hamgyong province. "The significance of this is that it has the potential to dramatically increase the threat posed by" its ballistic missiles.
New radar satellite images show North Korea's September 3 nuclear test was powerful enough to sink a roughly 85-acre area on the peak of a mountain above the tunnels where the test likely took place.
"I can not solve the deterrent problem reducing it from a triad".
Pyongyang was expected to test an intercontinental ballistic rocket last Sunday as North Koreans celebrated the country's 69th anniversary of its founding, but the test did not happen.
The missile, manufactured by Germany's Taurus Systems, has a maximum range of 500 kilometres and is equipped with stealth characteristics that will allow it to avoid radar detection before hitting North Korean targets, according to Seoul's Defence Ministry.
Information for this article was contributed by Choe Sang-Hun of The New York Times and by Kim Tong-Hyung, Hyung-jin Kim and Robert Burns of The Associated Press.