North Korea has carried out a third nuclear test in defiance of United Nations warnings.
The move prompted criticism from its sole major ally, China, and condemnation around the world.
The North Korean news agency said the underground test used a smaller, lighter nuclear device with greater explosive force than before.
Observers say it could take North Korea closer to building a warhead small enough to arm a long-range missile.
The UN Security Council will meet at 14:00 GMT to discuss the test and its ramifications, diplomats say.
It's the Iran connection that's the most worrying. There's at least a degree of cold rationality to the North Koreans: they're not about to nuke Seoul, or Tokyo. With the Iranian theocracy, and their terrorist proxies, all bets are off.