North Korea Conducted a Nuclear Test

An international nuclear test monitoring agency said on Tuesday that it had detected an "unusual seismic event" in North Korea, following weeks of speculation that a nuclear test was imminent in the country.

"We have detected an unusual seismic event in North Korea," said Annika Thunborg, a spokeswoman for the Comprehensive Nuclear-Test Ban Treaty Organization (CTBTO), an agency set up to monitor compliance with a ban on nuclear tests that has yet to come into effect.

The Vienna-based CTBTO said on Twitter that "our analysts are currently studying data."

The CTBTO is the world's independent body for monitoring possible breaches of the test ban, with more than 270 facilities established worldwide to pick up signs of any nuclear explosions.

Its stations use different kinds of technology to detect seismic indications as well as radioactive particles in the atmosphere.

Meanwhile, a South Korean government official said the North had conducted a nuclear test, escalating tensions with an international community that has sought to curb the totalitarian state’s atomic ambitions.

“Artificial quake tremors from North Korea are likely to be a nuclear test but we will need to take a closer look at the details to be sure,” South Korean Defense Ministry spokesman Kim Min Seok said by phone.

A 5.1-magnitude artificial earthquake hit North Hamgyong Province at 11:58 a.m. local time, Yonhap News reported without citing anyone. The U.S. Geological Survey said it registered a 4.9 magnitude quake in North Korea.

South Korea’s currency slipped after the reports, with the won down 0.2 percent at 1094.43 per dollar as of 12:29 p.m. Seoul time. The Kospi index of stocks dropped 0.4 percent.

The MSCI Asia Pacific Index retained its gains, with markets including Hong Kong and Singapore off for lunar new year celebrations.

The temblor hit at 11:58 a.m. local time, Yonhap said. North Korea has conducted two nuclear tests in recent years. Its test site is located in Hamgyong Provice.

The epicenter of the seismic activity, which was only one kilometer below the Earth's surface, was close to the North's known nuclear test site.

"We've been informed by the South Koreans that there's been a [North Korean] nuclear test," a U.N. Security Council diplomat told Reuters on condition of anonymity.

An international nuclear test monitoring agency said the location of the seismic event was "roughly congruent with" 2006 and 2008 tests carried out by the reclusive state and had "clear explosion-like characteristics."

North Korea, which had been threatening a third nuclear test, had informed Beijing and Washington on Monday of plans to undertake a test, South Korea's Yonhap news agency reported.

The isolated state, which is banned under U.N. Security Council resolutions from developing nuclear and missile technology, did not make any immediate comment.

North Korea is not prone to seismic activity and it may take hours or even days to determine officially whether a nuclear test had been conducted.

South Korea's defense ministry said the North Korean seismic event could be the result of a 6-7 kiloton or stronger nuclear blast. South Korea's President Lee Myung-bak called a national security council meeting for 0400 GMT.

North Korea successfully launched a long-range rocket in December in violation of U.N. resolutions that banned it from developing missile or nuclear technology after nuclear tests in 2006 and 2009.

It announced plans for a third nuclear test in response to the sanctions imposed in January after the rocket launch, although satellite imagery indicated it has been readying its test site for more than a year.