North Korea said it successfully conducted a nuclear test on Monday, a move certain to further isolate the prickly state, which argues it has no choice but to build an atomic arsenal to protect itself in a hostile world.

The test, the North's second, follows years of on-off negotiations with regional powers, which have been pressing the impoverished state to give up its nuclear ambitions in return for massive aid and an end to the country's pariah status.

Ratcheting up tensions further, North Korea fired a short-range missile just hours later, the Yonhap news agency reported, citing a diplomatic source. The missile was fired from North Korea's east coast missile site at Musudan-ri.

The U.N. Security Council would hold an emergency meeting later on Monday in the wake of the nuclear test, Russia's ambassador to the United Nations said.

(North Korea) successfully conducted one more underground nuclear test on May 25 as part of the measures to bolster up its nuclear deterrent for self-defense in every way, the North's official KCNA news agency said.

It added that the underground test was safely conducted on a new higher level in terms of its explosive power and technology of its control.

The U.S. Geological Survey said it had detected a 4.7-magnitude quake in an area close to where the test site is thought to be.

However, as with the first nuclear test by the communist state in October 2006, it could take some time before the outside world is able to gauge how successful it was. The first one was seen as only a partial success.

The news knocked South Korean financial markets, with the main share index dropping 4 percent at one stage and the won falling more than 1 percent against the dollar on fears the test would raise tension in a region which accounts for one-sixth of the global economy.

South Korean financial markets later recovered much of their earlier losses as investors bet that any direct impact on markets would be short-lived unless there was actual military conflict.

Market reaction elsewhere was limited, with safe-haven gold prices falling slightly on the day and Japan's Nikkei average clinging to gains.

The reported test appears to be aimed at securing ultimate endorsement of its nuclear power status from the United States and bringing Washington to the negotiation table, said Kim Sung-han, a professor at Korea University.

It could increase investor concerns about South Korea as the test may further worsen already soured inter-Korea relations, he added.

However, several analysts said they expected the impact on financial markets to be short-lived.


Japan's chief cabinet secretary, Takeo Kawamura, said the test was unacceptable and a violation of a U.N. Security Council Resolution.

North Korea had for weeks threatened to conduct the test in response to tighter international sanctions following its launch of a rocket in April. Pyongyang said that launch put a communications satellite into space, but Western nations said it was a disguised long-range missile.

Following the added sanctions, Pyongyang also said it would no longer be a party to six-nation talks on giving up its nuclear weapons program.

North Korea's strategic objective hasn't changed. That objective is to win the attention of the Obama administration, to push the North Korea issue up the agenda, said Xu Guangyu, a researcher at the China Arms Control and Disarmament Association.

Xu said China, the nearest Pyongyang has to a powerful ally, might support a U.N. resolution censuring North Korea but would not back much harsher sanctions.

China's goal is to ensure that the six-party talks process does not fall apart. Stricter sanctions are not going to achieve that objective, Xu said.

Some analysts have said the test may also be aimed at boosting the position at home of leader Kim Jong-il, who is widely believed to have suffered a stroke last year.

Several say Kim, who succeeded his father to create the world's first communist dynasty, may be trying to secure the succession for one of his three sons and that a nuclear test in defiance of world opinion could help him win support from his hardline military to do so.

One has to wonder if this is part of the internal political transition that may be occurring inside North Korea, said Jim Walsh, an expert in international security and a research associate at the Massachusetts Institute of Technology.