The United Nations Security Council says it will "begin to work immediately" to take action against North Korea. The UN believes a nuclear test that North Korea carried out on Wednesday could be a hydrogen bomb. This was the fourth time since 2006 that North Korea has tested a nuclear bomb, but it could be the first time it has tested a hydrogen bomb. A hydrogen bomb is a lot more powerful than the atomic bombs dropped on Japan during World War II. The UN said of North Korea's test that: "A clear threat to international peace and security continues to exist." However, the UN has not said what action it would take against North Korea, nor when any measures would be put in place.
Not all countries agree on what to do about North Korea's latest nuclear test. The USA said it does not think the test was a hydrogen bomb because the explosion was too small. A South Korean politician agreed. However, both the USA and South Korea said the test was a dangerous move by North Korea. Japan wants the UN to act quickly to take action. Japan's ambassador to the UN said: "The authority and credibility of the [UN] will be put in question if it does not take these measures." China had strong words for North Korea. Its government said: "We strongly encourage North Korea to honour its de-nuclearisation promises and to stop taking any action that will make this situation worse."