SEOUL- North Korea conducted a second nuclear test on Monday that was far more powerful than its first one, triggering an emergency U.N. Security Council meeting on the hermit state's defiant act and drawing condemnation from around the globe.
Financial markets in Asia wobbled on briefly the news. Markets in the United States and Britain were closed for a holiday.
U.S. President Barack Obama said Pyongyang's attempts at developing nuclear weapons was a threat to international peace and security and the international community would need to respond.
The North's neighbour and long-time benefactor, China, said it was resolutely opposed to the test.
Russia, which also called the test a threat to regional security, said the blast was about equal in power to the U.S. atom bomb dropped on the Japanese city of Nagasaki in World War Two.
Ratcheting up tensions further, North Korea test-fired three short-range missiles just hours later, Yonhap news agency said.
North Korea's nuclear and ballistic missile programs pose a grave threat to the peace and security of the world, and I strongly condemn their reckless action, Obama said at the White House.
The United States and the international community must take action in response, he said.
Officials in Washington and Beijing said North Korea had warned their governments of the test about an hour before detonation but nearby Japan said it was not given advance notice.
Germany, France, Britain and the EU were among those condemning Pyongyang's act, while U.N. Secretary-General Ban Ki-moon said he was deeply worried. The U.N. Security Council was to hold emergency talks on Monday at 4 p.m. EDT (9 p.m. British time).
Monday's blast was up to 20 times more powerful than the North's first nuclear test about 2 1/2 years ago, 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 to sell its nuclear know-how to states such as Syria.
Iran, which the West accuses of secretly developing atomic weapons and which conducted a missile test last week, said it had no missile or nuclear cooperation with North Korea.
NORTH KOREAN LEVERAGE
Analysts said the North Korea's test also will serve to raise its 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 dealt 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 during 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.
North Korea already is 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 the 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.
The country's first nuclear test, in October 2006, was considered to have been relatively weak, about 1 kiloton, suggesting design problems.
SECURITY COUNCIL TO MEET
China Monday echoed concerns by other permanent members of the U.N. Security Council.
The Chinese side vehemently demands North Korea abides by its denuclearization promises, stop any actions which may worsen the situation and return to the six-party talks process, the Foreign Ministry said in a statement on its website (www.mfa.gov.cn).
The Chinese government calls on all sides to calmly and appropriately deal (with the situation).
Analysts said, however, Beijing was unlikely to back stronger sanctions as part of a new U.N. Security Council resolution.
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.