A man watches a TV news program on a public screen showing an image of North Korean leader Kim Jong Un while reporting North Korea's possible nuclear test in Tokyo Sunday, Sept. 3, 2017. South Korea's military said Sunday that North Korea is believed to have conducted its sixth nuclear test after it detected a strong earthquake, hours after Pyongyang claimed that its leader has inspected a hydrogen bomb meant for a new intercontinental ballistic missile. (AP Photo/Eugene Hoshiko)

A man watches a TV news program on a public screen showing an image of North Korean leader Kim Jong Un while reporting North Korea's possible nuclear test in Tokyo Sunday, Sept. 3, 2017. South Korea's military said Sunday that North Korea is believed to have conducted its sixth nuclear test after it detected a strong earthquake, hours after Pyongyang claimed that its leader has inspected a hydrogen bomb meant for a new intercontinental ballistic missile. (AP Photo/Eugene Hoshiko)

SEOUL, South Korea (AP) — The Latest on the tensions on the Korean Peninsula (all times local):

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4:10 p.m.

South Korea’s presidential office says the security chiefs for Seoul and Washington have spoken following North Korea’s sixth nuclear test.

The office says U.S. National Security Adviser H.R. McMaster spoke with his South Korean counterpart, Chung Eui-yong, for 20 minutes in an emergency phone call about an hour after the detonation.

North Korea’s nuclear test Sunday was apparently its most powerful yet. State-controlled media say it was a hydrogen bomb. South Korea’s weather agency says the apparent detonation set off a magnitude 5.7 earthquake, making the blast five to six times stronger than the North’s fifth test in September 2016.

3:45 p.m.

North Korean TV says the country has successfully conducted a test of a hydrogen bomb that is meant to be loaded into an intercontinental ballistic missile.

The TV anchor announced the test’s success on Korean Central Television, hours after Seoul and Tokyo detected unusual seismic activity at North Korea’s nuclear test site. The announcer says North Korea’s leader Kim Jong Un ordered the test.

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3:30 p.m.

South Korea’s weather agency says an apparent nuclear test by North Korea appears to have been several times stronger than its previous test.

The Korea Meteorological Administration estimated Sunday that the nuclear blast yield of the presumed test was between 50 to 60 kilotons, or five to six times stronger than the North Korea’s fifth test in September 2016.

North Korea is believed to have conducted a test after a magnitude 5.7 earthquake was detected earlier Sunday. The previous test created seismic waves with a magnitude of 5.0.

Japan’s defense minister says the larger magnitude of the earthquake suggests “capability significantly exceeding the last one.”

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2:55 p.m.

North Korea’s state broadcaster says an important announcement is coming at 3 p.m. in Pyongyang. That would be 3:30 p.m. in Seoul and Tokyo, and 2:30 a.m. EDT.

KRT did not give any details of the announcement, but it comes after earthquake activity was detected earlier Sunday in what is presumed to have been a North Korean nuclear test.

The apparent test came hours after North Korea said its leader had inspected a hydrogen bomb meant for a new intercontinental ballistic missile. The report could not be independently verified.

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2:30 p.m.

South Korea has refuted a news report that there was a second earthquake near North Korea’s nuclear test site.

The Korea Meteorological Administration said Sunday that it had not detected another quake.

South Korea’s Yonhap news service reported a second earthquake had happened eight minutes after the first, citing China’s earthquake agency.

South Korea’s military said earlier Sunday that North Korea is believed to have conducted its sixth nuclear test after seismic waves were detected with a magnitude of 5.7. That was revised up from an initial report of 5.6.

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1:40 p.m.

South Korea’s Yonhap news agency says a second quake was detected near North Korea’s nuclear test site.

The second quake measured 4.6.

South Korea’s military said earlier Sunday that North Korea is believed to have conducted its sixth nuclear test after it picked up seismic waves measuring 5.6. The U.S. Geological Survey called the first quake an explosion with a magnitude 6.3.

It came hours after North Korea claimed that its leader has inspected a hydrogen bomb meant for a new intercontinental ballistic missile.

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1:30 p.m.

South Korea’s military says North Korea is believed to have conducted its sixth nuclear test.

The Joint Chiefs of Staff in Seoul says in a statement South Korea’s military has strengthened monitoring and readiness and is mulling a variety of possible responses that could be pushed together with its ally the U.S.

The apparent test came just hours after North Korea claimed that its leader has inspected the loading of a hydrogen bomb into a new intercontinental ballistic missile.

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1:05 p.m.

South Korea’s Joint Chiefs of Staff says a magnitude 5.6 quake in North Korea was artificial and it’s analyzing whether the North conducted a nuclear test.

It says it detected a seismic wave from 12:34 p.m. to 12:36 p.m. around Punggyeri, North Korea.

The quake came just hours after North Korea claimed that its leader has inspected the loading of a hydrogen bomb into a new intercontinental ballistic missile.

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1 p.m.

South Korea’s Yonhap News agency says a magnitude 5.6 quake has occurred in North Korea.

It isn’t immediately clear whether North Korea has conducted its sixth nuclear test. North Korea conducted its fifth test last September.

The report came just hours after North Korea claimed that its leader has inspected the loading of a hydrogen bomb into a new intercontinental ballistic missile.

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10:45 a.m.

The White House says President Donald Trump spoke with Japan’s Prime Minister Shinzo Abe to discuss “ongoing efforts to maximize pressure on North Korea.”

The statement did not say whether the conversation came before or after the North’s latest claim that its leader has inspected the loading of a hydrogen bomb into a new intercontinental ballistic missile.

Sunday’s statement by the state-run Korean Central News Agency will raise already high worries on the Korean Peninsula and in Washington that the North is closer to its goal of an arsenal of viable nuclear ICBMs that can reach the U.S. mainland.

According to the White House statement, the two leaders reaffirmed the importance of close cooperation between the United States, Japan, and South Korea in the face of the growing threat from North Korea. Trump also noted that he looks forward to continued trilateral coordination on the margins of the United Nations General Assembly.