The United Nations Security Council says it will "begin to work immediately" to take action about against by during for in of on out to North Korea. The UN believes a nuclear test that North Korea carried about against by during for in of on out to 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 about against by during for in of on out to Japan about against by during for in of on out to World War II. The UN said about against by during for in of on out to North Korea's test that: "A clear threat about against by during for in of on out to international peace and security continues to exist." However, the UN has not said what action it would take about against by during for in of on out to North Korea, nor when any measures would be put about against by during for in of on out to place. Not all countries agree about against by during for in of on out to what to do about against by during for in of on out to 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 about against by during for in of on out to North Korea. Japan wants the UN to act quickly to take action. Japan's ambassador about against by during for in of on out to the UN said: "The authority and credibility about against by during for in of on out to the [UN] will be put about against by during for in of on out to question if it does not take these measures." China had strong words about against by during for in of on out to 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."