North Korea has "successfully" conducted a nuclear test today, according to its state media.
"We have successfully conducted another nuclear test on May 25 as part of the republic's measures to strengthen its nuclear deterrent," 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 news knocked South Korean financial markets with the main share index falling 4 per cent at one stage on fears the test will raise tension in a region which accounts for one sixth of the global economy.
"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.
North Korea has for weeks threatened to conduct the test - its first was in October 2006 - in response to tighter international sanctions following its launch of a rocket in April.
The communist state said that launch was to put a communications satellite into space. The international community said it was a disguised long-range missile.
Following the added sanctions, Pyongyang also said it would no longer be a party to regional talks on giving up attempts to build nuclear weapons in exchange for massive aid and an end to its status as a pariah state.
Some analysts have said the test may also be aimed at boosting the position at home of leader Kim Jong-il, 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 secure the succession for one of his three sons and that a nuclear test in defiance of world opinion could help him win support to do so from his hardline military.
South Korean President Lee Myung-bak called an emergency meeting of cabinet ministers over the test.
South Korea's Yonhap news agency also claimed in an unsourced report, that North Korea launched two additional short-range missiles, hours after Pyongyang announced it had conducted a successful nuclear test.
North Korea earlier fired a short-range missile off its east coast, Yonhap said.Reuse content