North Korea says it successfully conducts nuclear test

Kim Kwang Hyon / AP

On a large television screen in front of Pyongyang's railway station, a North Korean state television broadcaster announces Tuesday that North Korea has conducted a nuclear bomb test.

By Ian Johnston, Eric Baculinao and Arata Yamamoto, NBC News

North Korea declared Tuesday that it had carried out a test of a nuclear bomb after the detonation was detected by the U.S. Geological Survey.

The explosion was registered as a 5.1-magnitude seismic event by the USGS at 9:57 p.m. ET Monday.

The U.S. Office of the Director of National Intelligence said in a statement that the "intelligence community" was aware of "a seismic event with explosive characteristics in North Korea and we are evaluating all relevant information."

In a statement, President Barack Obama described the test as a "highly provocative act."

He said that -- following a "ballistic missile launch" by North Korea on Dec. 12 -- the test "undermines regional stability, violates North Korea's obligations under numerous United Nations Security Council resolutions, contravenes its [international] commitments … and increases the risk of proliferation."

"North Korea's nuclear weapons and ballistic missile programs constitute a threat to U.S. national security and to international peace and security," Obama said. "The United States remains vigilant in the face of North Korean provocations and steadfast in our defense commitments to allies in the region."

He said North Korea's "provocations do not make North Korea more secure" and the communist state had "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," Obama said, adding the U.S. would work with the international community to "pursue firm action."

'Unacceptable threat'South Korea's government said in a statement that "the nuclear test poses a direct challenge to the whole international community as well as an unacceptable threat to the peace and security of the Korean Peninsula and Northeast Asia."

"Standing firm on its consistent principle that it will not tolerate a nuclear North Korea, the [South Korean] Government … will cooperate closely with the international community and seek all necessary measures including actions by the United Nations Security Council in order to have North Korea abandon its nuclear ambition,” it added.

South Korea is president of the Security Council this month.

The statement added that South Korea would maintain "a high readiness posture against any possible provocation by North Korea."

It said the government would "also accelerate expanding its military capability, including deploying at an early stage its extended-range missiles, currently being developed, which cover all of North Korea."

Japan's Prime Minister Shinzo Abe said the test was "extremely regrettable and we strongly protest this act."

Japan launched several planes to test for nuclear particles in the air, Defense Minister Itsunori Onodera said. He described the test as a "major provocation not only towards the safety of our country but also against the international community."

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