North Korea says it set off an underground nuclear explosion Monday, making good on a recent promise to carry out a nuclear test to bolster its defenses.
The United States says a North Korean nuclear test would be a provocative act that would aggravate tensions in northeast Asia. President Bush's spokesman, Tony Snow, says American officials are monitoring the situation closely, and he reaffirmed America's commitment to protect and defend its allies in Asia.
The U.N. Security Council is expected Monday to begin an urgent examination of Pyongyang's actions.
South Korea raised its military alert level after the nuclear-test announcement. The Korean peninsula has been particularly tense since Saturday, when South Korean forces fired at North Korean troops who had crossed the Demilitarized Zone.
The North Korean news agency KCNA declared the nuclear test was carried out successfully and safely, with no radiation leakage from the blast site deep underground.
Most governments are awaiting confirmation that North Korea did in fact detonate a small nuclear explosion. In Moscow, Russian military experts said to Itar-Tass news agency that they are certain that North Korea's claim was correct.
The explosion that rocked northeastern North Korea this morning at 0136 UTC apparently had the effect of a small to moderate earthquake, with a magnitude between 3.5 and 4.2.
Japan says the seismic activity that it detected in North Korea was not caused by an earthquake. U.S. and South Korean scientists also detected seismic waves in the same area, at the same time.
South Korea says it will respond sternly to North Korea. A spokesman for President Roh Moo-hyun says Seoul will not tolerate a nuclear-armed North.
Mr. Roh convened an emergency security meeting in Seoul to discuss the issue.
Some information for this report provided by AP, AFP and Reuters.