By Jonathan Thatcher
SEOUL (Reuters) - North Korea conducted a second and far more powerful nuclear test Monday, triggering an emergency U.N. Security Council meeting on the hermit state's defiant act, but financial markets wobbled only briefly on the news.
Prime Minister Gordon Brown called North Korea "a danger to the world," and Russia said the blast was about equal in power to the U.S. atom bomb dropped on the Japanese city of Nagasaki in 1945 at the end of World War Two.
Monday's blast was up to 20 times more powerful than the North's first nuclear test about 2- years, underscoring the advances in its nuclear program despite multilateral talks on ending Pyongyang's nuclear weapons ambitions.
The latest test will confound the international community, which has for years tried a mixture of huge aid pledges and tough economic sanctions to persuade the impoverished North to give up efforts to build a nuclear arsenal.
It is also bound to raise concerns about proliferation, a major worry of the United States which has in the past accused Pyongyang of trying try to sell its nuclear know-how to states such as Syria.
Analysts said the test will also serve to raise North Korea's leverage in any negotiations with the United States.
It comes as speculation has mounted that leader Kim Jong-il, his health uncertain after reports of a stroke last year, wants to strengthen an already iron grip on power so he can better secure the succession for one of his three sons.
The nuclear test was another blow to South Korean markets, already unsettled by fears of domestic unrest after former President Roh Moo-hyun, who had been questioned over his links to a corruption scandal, jumped to his death at the weekend.
South Korea's main stock market index fell more than 6 percent at one stage on worries by some that investors would flee.
But the decline was short-lived and analysts said investors were used to the North's repeated sabre-rattling, even as it became more aggressive, and would likely panic only if there was military conflict on a peninsula where 2 million troops face each other across one of the world's most heavily armed borders.
Ratcheting up tensions further, North Korea test-fired three short-range missiles just hours later, the Yonhap news agency reported.
NORTH SAYS "NUCLEAR DETERRENT"
North Korea is already so isolated there is little left with which to punish an autocratic government that has long been willing to take dealings with the outside world to the brink.
At home, its leaders repeatedly stress the threat from a hostile United States to justify heavy spending on the military that keeps them in power but which has meant deepening poverty, at times famine, for most of the rest of its 23 million people.
The official KCNA news agency said North had "successfully conducted one more underground nuclear test on May 25 as part of the measures to bolster up its nuclear deterrent for self-defence in every way."
A South Korean presidential aide said North Korea had given the United States advance notice of the latest test, which followed a partially successful long-range rocket launch last month.
The country's first nuclear test, in October 2006, was considered to have been relatively weak, about 1 kiloton, suggesting design problems.
Itar-Tass news agency quoted Russia's defence ministry as saying Monday's blast was up to 20 kilotons, about the same size as the U.S. atomic bomb dropped on Nagasaki in 1945.
Neighbour and long-time benefactor China said it was "resolutely opposed to" the test, echoing concern expressed by other permanent members of the Security Council which was due to hold an emergency meeting later Monday.
U.S. President Barack Obama said it was "a matter of grave concern to all nations" and warranted action by the international community.
European Union foreign policy chief Javier Solana called the test "irresponsible" but, like Obama, did not specify what actions the international community might take.
"North Korea's actions are more for international audience, especially the United States," Koh Yu-hwan, Dongguk University professor of North Korea studies, said.
"Hawkish military elements of the North Korean leadership want a stronger nuclear deterrence and status as a nuclear power before going to the negotiating table with the U.S."
ATTENTION GRABBING
North Korea had for weeks threatened to conduct the test in response to tighter international sanctions following its April launch of a rocket, widely seen as a disguised long-range missile that violated U.N. resolutions.
Following the tightened sanctions, Pyongyang also said it would no longer be a party to six-country 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.
Some analysts have said the test may also be aimed at boosting the position at home of leader Kim Jong-il.
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.
"North Korea can only be hawkish this time, because time's running out for Kim Jong-il. With the dire economy, North Korean public sentiment can go against succession," said Jang Cheol-hyeon, a researcher at the Institute for National Security Strategy and a former North Korean official.
(Reporting by Kim Junghyun, Rhee So-eui, Park Jongyoun, Marie-France Han, Jon Herskovitz, Miyoung Kim, Angela Moon, Kim Yeon-hee, Yoo Choonsik and Jack Kim in SEOUL, Chris Buckley in BEIJING, Linda Sieg in TOKYO, Connor Humphries in MOSCOW, Editing by John Chalmers and Jeremy Laurence)
