Updated

The latest on North Korea's announcement that is has conducted a hydrogen bomb test (all times local):

3:45 p.m.

In Pyongyang, North Koreans reacted enthusiastically to the news that the country has carried out its fourth nuclear test since 2006.

Kim Sok Chol, a 32-year-old man who watched the TV announcement on a big screen at the train station square, told The Associated Press that he does not know much about what a hydrogen bomb is, but added that "since we have it, the U.S. will not attack us. I think the first successful H-bomb test is a great national event."

Ri Sol Yong, a 22-year-old university student, said the test "gives us more national pride."

She said, "Thanks to the fact that our country is a nuclear weapons state, I can study at the university without any worries. If we didn't have powerful nuclear weapons, we would already have been turned into the slaves of the U.S."

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2:25 p.m.

The White House says it can't confirm a North Korean nuclear test, but said it would condemn such a test as a violation of U.N. Security Council resolutions.

North Korea said Wednesday it has conducted a hydrogen bomb test — a move that would put the country a step closer toward improving its still-limited nuclear arsenal.

National Security Council spokesman Ned Price says the U.S. is "aware of seismic activity on the Korean Peninsula in the vicinity of a known North Korean nuclear test site and have seen Pyongyang's claims of a nuclear test."

He calls on North Korea to abide by its international obligations and commitments and said the U.S. consistently made clear that it will not accept North Korea as a nuclear state and will continue to defend U.S. allies in the region.

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2:10 p.m.

Crowds dressed in thick winter coats have gathered outside a large video screen near a Pyongyang train station to cheer and take video and photos on their mobile phones of the state TV anchor announcing the country had carried out a nuclear test.

Some people raised their hands and applauded. Many smiled and cheered.

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2 p.m.

South Korea says it will consult with allies and regional powers to get North Korea to face the consequences of the nuclear test it said it had carried out, such as additional U.N. sanctions.

Presidential security official Cho Tae-yong says: "We strongly condemn" the North's fourth bomb test.

He says North Korea must abide by U.N. resolutions that require the country to scrap its nuclear and ballistic missile programs completely and irreversibly.

South Korea's Defense Ministry also says it is bolstering security and monitoring on North Korea.

— Hyunh-jin Kim, Seoul, South Korea

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1:45 p.m.

The head of the U.N. Comprehensive Test Ban Treaty Organization, which monitors worldwide for nuclear testing, says if confirmed, a nuclear test by North Korea would be a breach of the treaty and a grave threat to international peace and security.

Lassina Zerbo says in a statement that the universally accepted norm against nuclear testing has been respected by 183 countries since 1996.

Zerbo urged North Korea to refrain from further nuclear testing and join the 183 states who have signed the treaty.

— George Jahn, Vienna

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1:40 p.m.

Japanese Prime Minister Shinzo Abe says the North Korean announcement of a hydrogen bomb test is a threat to his nation's safety.

Abe told reporters: "We absolutely cannot allow this, and condemn it strongly."

He called it a violation of the U.N. Security Council agreements that is against the global efforts toward nuclear disarmament.

Abe says he will take "strong action," work with other nations, the U.S., South Korea, China and Russia, as well as through the U.N.

— Yuri Kageyama, Tokyo

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1:25 p.m.

The U.N. organization monitoring the world for signs of nuclear testing says it has detected "an unusual event in the Korean Peninsula."

The head of the Comprehensive Test Ban Treaty Organization Lassina Zerbo says in a statement: "Our International Monitoring System detected an unusual seismic event in the Korean Peninsula at latitude 41.27 longitude 129.10."

The location on the map places the epicenter at North Korea's Pyunggye-ri testing site in its northeastern mountains, where all of its nuclear tests have been conducted.

North Korea said Wednesday it had conducted a hydrogen bomb test, which, if confirmed, would put Pyongyang a big step closer toward improving its still-limited nuclear arsenal.

— George Jahn, Vienna