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.
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.
Such a strike would involve detonating a bomb in the atmosphere, instead of firing a long-range missile at a major US city.
The Arms Control Association estimates the US has 6,800 nuclear warheads, while Russia has closer to 7,000.
For the first time, North Korea also specifically mentioned the possibility of a electromagnetic pulse, or EMP, attack.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 UK has around 120, of which 40 are deployed at sea on Vanguard class ballistic missile submarines, while France has around 300 and China 270.India and Pakistan are estimated to have around 120 nuclear missiles, and Israel is suspected of having around 80.