AP: On Monday, the country's official Korean Central News Agency said the regime "successfully conducted one more underground nuclear test on May 25 as part of measures to bolster its nuclear deterrent for self-defense."
The regime boasted that the test was conducted "on a new higher level in terms of its explosive power and technology of its control."
South Korean President Lee Myung-bak convened an emergency security session. His spokesman, Lee Dong-kwan, confirmed that a North Korean nuclear test was possible.
In Washington, State Department spokesman Andy Laine said: "At this point, we've seen the reports and we're trying to get more information, but we're not able to confirm at this time." ...
Seismologists from the U.S., South Korea and Japan reported activity shortly after 9:50 a.m. in a northeastern area where North Korea conducted its first nuclear test in 2006.
The Japan Meteorological Agency measured the seismic activity at magnitude-5.3. Quake expert Gen Aoki noted that its depth was "very shallow."
"The area is not active seismically so it is highly possible that it could be an artificial quake," Aoki said in Tokyo.
In Seoul, the Korea Institute of Geoscience and Mineral Resources reported seismic activity in Kilju in North Hamgyong Province—the same area where North Korea carried out a nuclear test in October 2006.
Seismological measurements back North Korea's claim that the test was far stronger than in 2006.
At the Chinese border city of Yanji, 130 miles (200 kilometers) northwest from the test site, an emergency siren sounded shortly before 9 a.m. when officials thought an earthquake occurred. A receptionist at Yanji's International Hotel said she and several hotel guests felt the ground tremble.
An official at Yanji's government seismological bureau, who declined to give his name, said his agency confirmed that some type of explosion occurred, "but it is hard to say what kind of blast it was."
North Korea's 2006 test measured magnitude-3.6, an official at the Korea Meteorological Administration in Seoul said. He spoke on condition of anonymity, citing department policy.
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