North Korea says it tested nuke device underground

SEOUL, South Korea — North Korea announced today 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, northeast North Korea, said Lee Dong-Kwan, spokesman of the office of President Lee Myung-Bak of South Korea.

Seismologists from the United States and Japan also reported earthquakes in a northeastern area, where North Korea conducted a nuclear test in 2006.

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 South Korea's stock index plunging four percentage points within minutes.

North Korea conducted its first nuclear test Oct. 9, 2006, and it had given some advance notice of its intention to test a device.

It recently threatened to conduct a second test, citing what it called Washington's "hostilities" against the isolated Communist regime.

The test came against a backdrop of heightened U.S.-North Korean tensions; the U.S. keeps a heavy military deployment in South Korea.

Two U.S. journalists are to be tried June 4 in North Korea, charged with illegal entry into the North and "hostile acts." The female journalists, who work for San Francisco-based Current TV — a media venture founded by former Vice President Al Gore — were detained March 17 near the border while reporting on refugees living in China.

That case in particular has aggravated tensions between Pyongyang and Washington, which already were strained after the North launched a long-range rocket 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.

According to 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, 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 hours before Bosworth was to arrive in Seoul.

Information from The Associated Press

is included in this report.