SEOUL, South Korea — North Korea, in a broadcast on its state-run television network, confirmed it has successfully tested a hydrogen bomb meant for intercontinental ballistic missiles, several media outlets reported Sunday.
Seismological data from the United States Geological Survey showed that an explosion caused a 6.3-magnitude tremor in the northeastern section of North Korea, close to its Punggey-ri nuclear test site.
South Korea's meteorological agency called it a "man-made" earthquake.
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South Korea will hold a National Security Council meeting Sunday to discuss the incident, according to South Korea's Presidential office. The meeting will be presided by President Moon Jae-in, CNN reported.
U.S. National Security Advisor H.R. McMaster and South Korean National Security Office chief Chung Eui-yong held a 20-minute phone call to discuss North Korea's nuclear test, the Yonhap news agency reported, citing South Korea's presidential office.
Sunday morning, President Donald Trump said in a series of tweets that North Korea was "a rogue nation" that has become "a great threat and embarrassment to China." The president also tweeted that North Korea's words and actions "continue to be very hostile and dangerous" to the United States.
"South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!" Trump tweeted.
Chung Eui-yong, the chief security advisor for South Korean president Moon Jae-in, said his country will seek diplomatic measures to "completely isolate" North Korea.
"North Korea today ignored the repeated warnings from us and the international society and conducted a stronger nuclear test than before," Chung told reporters.
Earlier, the Japan Meteorological Agency had observed a magnitude-6.1 tremor in North Korea, which showed a different waveform from a natural quake.
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"The government confirms that North Korea conducted a nuclear test after examining information from the weather agency and other information," said Taro Kono, Japan's foreign minister.
Lassina Zerbo, the Executive Secretary of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), says data from North Korea's nuclear test indicates that the country's nuclear program is "advancing rapidly."
"It constitutes yet another breach of the universally accepted norm against nuclear testing; a norm that has been respected by all countries but one since 1996," Zerbo said. "It also underlines yet again the urgent need for the international community to act on putting in place a legally binding ban on nuclear testing once and for all. I urge the DPRK to refrain from further nuclear testing and to join the 183 States Signatories who have signed the Comprehensive Nuclear-Test-Ban Treaty."
China's Foreign Ministry on Sunday urged North Korea to stop its "wrong" actions, Reuters reported. In a statement, the ministry said on its website that China "resolutely opposed" and "strongly condemned" North Korea's actions. The ministry urged North Korea to respect U.N. Security Council resolutions, Reuters reported.
Russia's foreign ministry said North Korea's action "deserves the strongest condemnation."
In a statement Sunday, the ministry urged "immediate dialogue and negotiations." It added that Russia is ready to participate in negotiations, "including in the context of the Russian-Chinese road map."
Under that proposal, North Korea would suspend nuclear and missile tests in exchange for the U.S. and South Korea suspending their joint military exercises, CNN reported.