美国有线新闻 CNN 朝鲜宣布成功进行氢弹试验 威力远大于前（在线收听）

Once again, North Korea has defied international demands to give up its nuclear and missile programs. They're illegal, as far as the United Nations is concerned. They're a right as far as North Korea is concerned.

And the communist country said on Sunday that it had successfully tested out a hydrogen bomb, an extremely dangerous nuclear weapon. It was apparently tested underground, causing an earthquake of magnitude 6.3, a strong tremor.

And North Korea looks like it's getting ready to launch more test missiles, according to South Korea. That country has strengthened an American made missile defense system. It says the U.S. is going to increase its military presence in the region.

This would be the sixth time that North Korea has tested a nuclear weapon. But it appears to be the first time it's tested one this powerful.

SUBTITLE: North Korea and the H-Bomb.

PAULA HANCOCKS, CNN INTERNATIONAL CORRESPONDENT: Hydrogen bombs have never been used before in warfare. Atomic bombs have. This is what the U.S. struck on Nagasaki and Hiroshima back in 1945, ultimately killing more than 200,000 people. But the H-bomb is at least 100 times more powerful than the A-bomb. The H-bomb has a far larger yield than traditional weapons, meaning that devices can be smaller, while causing greater devastation.

Atomic bombs used a process called fission to split plutonium or uranium into smaller atoms and a chain reaction releasing massive amounts of energy. Hydrogen bombs used fusion, instead of splitting the atoms, it combines small atoms like hydrogen. Essentially, it's two bombs in one.

North Korea first claimed back in January 2016 it had successfully tested a hydrogen bomb. If it does in fact have this capability today, it has joined a very select club. Only the U.S., Russia, the U.K., France, and China have carried out confirmed tests of hydrogen bombs.