North Korea says it has carried out its first test of a nuclear weapon, the state news agency (KCNA) has reported.
It said the underground test, carried out in defiance of international warnings, was a success and had not resulted in any leak of radiation.
Pyongyang triggered an international outcry last week, when it announced plans to carry out the test.
Japan said if the test was confirmed it would be a "grave threat", while China denounced the action as "brazen".
Both countries had said in a joint statement ahead of the reported test that they would not tolerate such an action.
The White House condemned North Korea's nuclear test as a "provocative act", while South Korea said it would "sternly respond".
The South Korean armed forces have been put on a heightened state of alert, and President Roh Moo-hyun has called an emergency meeting of the National Security Council.
'Historic event'
There has been no official confirmation of the test, but the US Geological Survey said it had detected a 4.2 magnitude quake in North Korea that coincided with the claimed test.
South Korea's Yonhap news agency is reporting that the test took place in Gilju in Hamgyong province at 1036 (0136 GMT).
A South Korean official said an 3.5 magnitude seismic tremor had been detected in north Hamgyong province, in the north-east of North Korea.
When it announced the test, KCNA described it as an "historic event that brought happiness to our military and people".
"The nuclear test will contribute to maintaining peace and stability in the Korean peninsula and surrounding region," KCNA said.
The region has been on high alert since North Korea announced last week that it would conduct a nuclear test.
Japan's Prime Minister Shinzo Abe is in Seoul for a meeting with Mr Roh, a day after talks in Beijing.
Mr Abe said Japan wanted to co-ordinate its response with the South Koreans, and was also in contact with the US and China.
In Tokyo, ministers were called to an urgent meeting, and the government set up a special task force.
Vous en pensez quoi ? Ego surdimensionné d'un dictateur communiste ou début d'un conflit ? :??:
Moi perso ça commence à me faire flippé d'autant que ça s'est passé à tout juste 1000 km de chez moi :heink:
Edit : Une source en français :
Le monde
Update : Les premières réactions :
La Maison Blanche a condamné lundi l'essai nucléaire nord-coréen comme une provocation, s'il est confirmé, et réclamé une "action immédiate" du Conseil de sécurité de l'ONU.
La Corée du Sud a suspendu l'aide humanitaire qu'elle avait accordée à la Corée du Nord après les récentes inondations meurtières de l'été, en réprésailles à l'essai nucléaire annoncé lundi par le régime communiste, a indiqué l'agence sud-coréenne Yonhap.
Le Premier ministre japonais Shinzo Abe a qualifié lundi d'"impardonnable" l'essai nucléaire annoncé lundi par la Corée du Nord, selon l'agence sud-coréenne Yonhap.
Plus surprenante :
La Chine, par la voix de son ministère des Affaires étrangères, a officiellement condamné lundi l'essai nucléaire nord-coréen.