North Korea released pictures of Kim Jong-un smiling as he inspects what it says is a thermonuclear bomb in a propaganda drive that coincided with its claim his regime has successfully detonated its most powerful nuclear weapon ever.
The 33-year-old dictator is shown sizing up the device during a visit to the country's Nuclear Weapons Institute with five of his subordinates.
The uniformed men surrounding him take notes as he touches the silver metal contraption and looks over its red, black and yellow wires while it is mounted near to a diagram of a bomb loaded inside a cone.
The North Korean Central News Agency said the leader was inspecting "an H-bomb to be loaded into new ICBM (intercontinental ballistic missile)", but there is no way to independently verify the claims.
They said the weapon could generate hundreds of kilotons of explosive power, describing it as a "thermonuclear nuke with great destructive power which can be detonated even at high altitudes for super-powerful EMP (electromagnetic pulse) attack according to strategic goals".
Pyongyang said it successfully detonated a nuclear weapon meant for an intercontinental ballistic missile on Sunday.
The announcement came a few hours after international seismic agencies detected a manmade earthquake in the secretive state, which Japanese and South Korean officials said was around 10 times more powerful than the tremor picked up after its last nuclear weapon test a year ago.
An earthquake registering 6.3 was detected just before 7am BST 75km (45 miles) north-northwest of Kimchaek, where previous tests have been carried out.
Analysts fear the development could signify a significant step forward in the North's quest for a viable nuclear missile capable of striking anywhere in the US.
South Korea's President is to chair a National Security Council meeting. Its military said it has strengthened its monitoring and readiness while considering a variety of possible responses in collaboration with the US.
North Korea carried out two nuclear tests last year, the last nearly a year ago, on the 9 September anniversary of the nation's founding.
The country, which carries out its nuclear and missile programmes in defiance of United Nations Security Council resolutions and sanctions, said in an announcement on state television that a hydrogen bomb test ordered by leader Kim Jong Un was a "perfect success" and a "meaningful" step in completing the country's nuclear weapons programmes.
The bomb was designed to be mounted on its newly developed intercontinental ballistic missile (ICBM), they claimed.
China, North Korea's sole major ally, said it strongly condemned the nuclear test. The United States has repeatedly urged Beijing to do more to rein in its neighbour.
South Korean President Moon Jae-in said Seoul would push for strong steps to further isolate the North, including new UN sanctions, news agency Yonhap reported.
Japan also raised the prospect of further sanctions, with Chief Cabinet Secretary Yoshihide Suga saying that curbs on North Korea's oil trade would be on the table.
A U.S. official who studies North Korea's military and politics said it was too early to determine if a test supported the North's claim that it has succeeded in developing a thermonuclear weapon, "much less one that could be mounted on an ICBM and re-enter Earth's atmosphere without burning up".
The latest nuclear test comes amid heightened regional tension following Pyongyang's two tests of intercontinental ballistic missiles (ICBM) in July that potentially could fly about 10,000 km (6,200 miles), putting many parts of the mainland United States within range.
Additional reporting by Reuters
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