SEOUL, South Korea — North Korea announced today that it had successfully conducted its second nuclear test, defying international warnings and drastically raising the stakes in a global effort to get the recalcitrant Communist state to give up its nuclear weapons program.
The North's official news agency, KCNA, said the country had conducted an "underground" nuclear test as "part of measures to bolster its nuclear deterrent for self-defense."
The announcement came moments after the South Korean government's geological sensors had detected an artificially triggered tremor emanating from Kilju in northeast North Korea, said Lee Dong-kwan, spokesman for President Lee Myung-bak of South Korea, which convened an emergency security session.
The spokesman said "intelligence officials of South Korea and the United States are analyzing the data and closely monitoring the situation."
Word of the nuclear test sent a shudder through Asian financial markets, with Korea's stock index plunging four percentage points within minutes.
North Korea conducted its first nuclear test on Oct. 9, 2006, and it had given some advance notice of its intention to test a device. That initial test also was in the northeast.
North Korea recently threatened to conduct a second nuclear test, citing what it called Washington's "hostilities" against the isolated Communist regime.
The test came against a backdrop of heightened tensions between North Korea and the United States, which keeps a heavy military deployment in South Korea.
Two American journalists are scheduled to be tried June 4 in North Korea, charged with illegal entry into the North and "hostile acts." That case in particular has aggravated tensions between Pyongyang and Washington, which were already strained after the North launched a long-range rocket on April 5.
After that launching, Washington pressed the U.N. Security Council to tighten sanctions on the North. In retaliation, Pyongyang expelled U.N. nuclear monitors, while threatening to restart a plant that makes weapons-grade plutonium and to conduct a nuclear test.
This month, one day after a U.S. diplomat offered new talks on North Korea's nuclear program, the North said it had become useless to talk further with the United States.
"The study of the policy pursued by the Obama administration for the past 100 days since its emergence made it clear that the U.S. hostile policy toward the DPRK remains unchanged," the North Korean Foreign Ministry said, using the initials for the country's official name, the Democratic People's Republic of Korea.
In comments carried by KCNA, the ministry said: "There is nothing to be gained by sitting down together with a party that continues to view us with hostility."
The rebuff came as Stephen Bosworth, the U.S. special envoy on North Korea, began a trip to Asia with a fresh offer of dialogue. The North's vow to "bolster its nuclear deterrent" came just hours before Bosworth was due to arrive in Seoul.
In Washington, State Department spokesman Andy Laine said the U.S. government had no confirmation of a new nuclear test.
"At this point we've seen the reports and we're trying to get more information, but we're not able to confirm at this time," Laine said.
Information from the Associated Press was used in this report.