SEOUL, South Korea -- North Korea said today it has performed its first-ever nuclear weapons test and the blast had been successfully set off underground with no radioactive leakage from the site.
An official at South Korea's seismic monitoring center confirmed a magnitude-3.6 tremor felt at the time North Korea said it conducted the test was not a natural occurrence. The official spoke on condition his name not be used, because he was not authorized to talk about the sensitive information to the media.
Japanese Prime Minister Shinzo Abe said that information still needs to collected and analyzed to determine whether North Korea truly conducted its first nuclear test.
U.S. and South Korean officials could not immediately confirm the report.
South Korea's Defense Ministry said the alert level of the military had been raised in response to the claimed nuclear test. The North said last week it would conduct a test, sparking regional concern and frantic diplomatic efforts aimed at dissuading Pyongyang from such a move. North Korea has long claimed to have nuclear weapons, but had never before performed a known test to prove its arsenal.
The North's official Korean Central News Agency said the underground test was performed successfully.
"It marks a historic event as it greatly encouraged and pleased the ... people that have wished to have powerful self-reliant defense capability," the KCNA statement said.
"It will contribute to defending the peace and stability on the Korean Peninsula and in the area around it."
South Korean intelligence officials said the seismic wave had been detected in North Hamkyung province, according to South Korea's Yonhap news agency. It said the test was conducted at 10:36 a.m. (8:36 p.m. CST Sunday) in Hwaderi near Kilju city on the northeast coast, citing defense officials.
North Korean scientists "successfully conducted an underground nuclear test under secure conditions," the KCNA report said, adding this was "a stirring time when all the people of the country are making a great leap forward in the building of a great prosperous powerful socialist nation."
The U.S. Geological Survey said it had detected no seismic activity in North Korea, although it was not clear whether a blast would be strong enough for its sensors.
On Sunday night, U.S. government officials said a wide range of agencies were looking into the report of the nuclear test, which officials were taking seriously.
South Korean President Roh Moo-hyun has convened a meeting of security advisers over the issue, Yonhap reported, and intelligence over the test has been exchanged between concerned countries.
Kyodo News agency reported that the Japanese government has set up a taskforce in response to reports of the test.
The North has refused for a year to attend international talks aimed at persuading it to disarm. The country pulled out of the Nuclear Nonproliferation Treaty in 2003 after U.S. officials accused it of a secret nuclear program, allegedly violating an earlier nuclear pact between Washington and Pyongyang.
Speculation over a possible North Korean test arose earlier this year after U.S. and Japanese reports cited suspicious activity at a suspected underground test site.