JEAN H. LEE
Associated Press Writer SEOUL, South Korea—North Korea claimed it carried out a powerful underground nuclear test Monday — much larger than one conducted in 2006 — a major provocation in the escalating international standoff over its rogue nuclear and missile programs.
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 country's official Korean Central News Agency said.
Russia's Defense Ministry confirmed an atomic explosion at 9:54 a.m. (0054 GMT) in northeastern North Korea, estimating the blast's yield at 10 to 20 kilotons — comparable to the bombs that flattened Hiroshima and Nagasaki.
Hours later, the regime test-fired three short-range, ground-to-air missiles, the Yonhap news agency reported, citing unnamed sources. U.N. Security Council resolutions bar North Korea from engaging in any ballistic missile-related activity.
President Barack Obama called the moves "blatant defiance" of the Security Council and a violation of international law that would only further isolate North Korea.
North Korea's claims "are a matter of grave concern to all nations," he said, calling for international action in a statement from Washington. "North Korea's attempts to develop nuclear weapons, as well as its ballistic missile program, constitute a threat to international peace and security."
The U.N. chief said Monday that if North Korea's claim can be confirmed, its announcement of a second nuclear test would represent "a clear violation" of a United Nations Security Council resolution.
"I sincerely hope that the Security Council will take necessary corresponding measures," U.N. Secretary-General Ban Ki-moon told The Associated Press, declining to specify what further moves, or sanctions, he would urge the 15 council members to take.
The council scheduled emergency consultations on North Korea's actions for Monday afternoon.
British Prime Minister Gordon Brown condemned the test as "erroneous, misguided and a danger to the world."
Japanese Prime Minister Taro Aso said the Security Council will meet at 4:30 p.m. Monday in New York (2030 GMT).
"North Korea's nuclear test poses a grave challenge to nuclear nonproliferation and clearly violates U.N. Security Council resolutions," he said in Tokyo. "We are not tolerating this at all."
Even China, North Korea's traditional ally, issued rare criticism of Pyongyang, with the Foreign Ministry saying in a statement posted on its Web site that Beijing was "resolutely opposed" to the test.
Russia said the test violated a U.N. Security Council resolution that requires North Korea to refrain from nuclear tests. Moscow's Foreign Ministry called the test "a serious blow to international efforts" to prevent the spread of nuclear weapons.
North Korea's bold defiance raises the stakes in the standoff over its nuclear program. In the past two months, Pyongyang has launched a rocket despite international calls for restraint; abandoned international nuclear negotiations; restarted its nuclear plants; and warned it would carry out the atomic test as well as long-range missile tests.
The rise in tensions comes amid questions about who will succeed impoverished North Korea's authoritarian leader, 67-year-old Kim Jong Il, who is believed to have suffered a stroke last August. North Korea also has custody of two American journalists — accused of entering the country illegally and engaging in "hostile acts" — who are set to stand trial in Pyongyang on June 4.
"This is a political act more than a military act," said Jim Walsh, an international security expert at the Massachusetts Institute of Technology.
Walsh said domestic factors related to North Korea's political transition were likely the main factor.
Monday's atomic test was conducted about 50 miles (80 kilometers) northwest of the northern city of Kilju, Russian Defense Ministry spokesman Alexander Drobyshevsky said, speaking on state-run Rossiya television.
Kilju, in the northeastern province of North Hamgyong, is where North Korea conducted its first nuclear test in October 2006 in a surprise move that also angered China and drew wide-ranging sanctions from the Security Council.