North Korea says it carried out an underground nuclear explosion Monday. News of the nuclear test immediately drew a chorus of condemnation in Asia and around the world.
The United States said North Korea has engaged in a provocative act in defiance of the international community.
South Korea, whose forces exchanged gunfire with North Korean troops across the Demilitarized Zone Saturday, raised its military alert level soon after the nuclear test was announced.
The North Korean news agency gave few specific details about the nuclear explosion, apart from saying it was a successful test and that there was no radioactive leak in the area.
South Korea says it will respond "sternly" to North Korea's action. A spokesman for South Korean President Roh Moo-hyun says the Seoul government will not tolerate a nuclear-armed North.
Mr. Roh has convened an emergency security meeting in Seoul to discuss the issue.
South Korea and the United States say seismological instruments detected a earthquake-like tremor in North Korea at the time (0136 UTC) the test is said to have been conducted.
Pyongyang said last week that it intended to test a nuclear weapon to bolster its defenses against what the communist state calls U.S. hostility.
AP, AFP and Reuters.