U.S. President Barack Obama called North Korea's powerful underground nuclear test Monday a "blatant violation of international law" and said action must be taken against the regime.
North Korea's official news agency said the country had "successfully conducted one more underground nuclear test on May 25 as part of measures to bolster its nuclear deterrent for self-defense."
Later Monday, North Korea also reportedly test-fired three short-range, ground-to-air missiles.
At a press conference Monday morning, Obama said North Korea was contradicting its own prior commitments with Monday's test.
"North Korea was previously committed to abandoning its nuclear program," Obama said.
"Instead of following through on that commitment, it has chosen to ignore that commitment."
He said the United States and the international community must "take action" in response.
Russia's Defence Ministry confirmed that an atomic explosion took place in northeastern North Korea. Russian officials said the blasts yield was 10 to 20 kilotons, which is comparable to the bombs that flattened Hiroshima and Nagasaki.
North Korea has reportedly been incensed by UN condemnation of its April 5 rocket launch.
Since then, the regime had warned that it would restart its nuclear program and carry out an atomic test. North Korea also said it would carry out long-range missile tests.
Obama said the U.S. would work with its allies to combat North Korea's behaviour.
"North Korea will not find security and respect through threats and illegal weapons," Obama said.
He said North Korea has in fact deepened its own isolation.
"We will redouble our efforts toward a more robust international non-proliferation regime that all countries have a responsibility to meet," Obama said.
International community reacts
The UN Security Council will meet at 4:30 p.m. Monday in New York, Japanese Prime Minister Taro Aso said.
"North Korea's nuclear test poses a grave challenge to nuclear nonproliferation and clearly violates UN Security Council resolutions," Aso said in Tokyo. "We are not tolerating this at all."
In Britain, Prime Minister Gordon Brown also condemned the test on Monday.
Brown called the action "erroneous, misguided and a danger to the world."
"This act will undermine prospects for peace on the Korean peninsula and will do nothing for North Korea's security," he said.
"The international community will treat North Korea as a partner if it behaves responsibly. If it does not, then it can expect only renewed isolation."
Monday's test was reportedly held in the same location where North Korea conducted its first nuclear test in October 2006.
North Korea said Monday's test was conducted "on a new higher level in terms of its explosive power and technology of its control" than in 2006.
With files from The Associated Press
