North Korea Conducts Nuclear Weapons Test

North Korea has announced that it tested a nuclear weapon this morning, triggering an artificial earthquake with a magnitude of 4.7.

"We successfully conducted another underground nuclear test on May 25 as part of measures aimed at strengthening our self-defence nuclear deterrent in every way," said the state-run North Korean news wire.

"The latest nuclear test was safely conducted on a higher level in terms of explosive power and technology of its control and the results of the test helped satisfactorily settle the scientific and technological problems arising in further increasing the power of nuclear weapons and steadily developing nuclear technology," the report continued.

The test will "contribute to safeguarding our sovereignty and socialism and guaranteeing peace and safety on the Korean peninsula and the surrounding region," it added.

The tremors from an earthquake were detected just before ten o'clock, around 230 miles north east of Pyongyang at a depth of just over six miles, according to the United States Geological Survey.

Lee Myung-bak, the South Korean president, called an emergency National Security Council meeting to discuss the situation. "Both South Korea and US intelligence agencies are analysing and closely monitoring the situation," said a spokesman for his office.

He added that the South Korean government had been warned beforehand that a nuclear test was possible. At the end of last week, an unnamed South Korean Defence official was quoted saying that "brisk activity" had been detected along North Korea's northern coast and that "trucks mounted with mobile rocket launchers are on the move".

Taro Aso, the Japanese prime minister, said he would set up a task force in response to the test.

The Chinese Foreign ministry said it was investigating the situation and could not comment immediately. Diplomatic sources said they had been expecting a North Korean nuclear test, and said the rogue state was trying to increase pressure on the United States in a high-stakes negotiation.

"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.

North Korea has repeatedly warned in the past month that it intends to restart its nuclear programme and build up its arsenal of nuclear weapons. Pyongyang was furious in April after the United Nations Security Council issued a rebuke against it for testing a long-range missile. The United States believed the missile was a weapon capable of striking continental America.

Reports of the nuclear test hit South Korean financial markets and the main KOSPI share index was down four per cent, while the won dropped more than one per cent against the US dollar.

In October 2006, North Korea detonated a very small nuclear device which the Atomic Energy Commission estimated at "about or less than a kiloton". Doubts were raised about whether it was actually a nuclear weapon, since conventional arms could have generated a similar blast.

The test drew international condemnation, including from China, Pyongyang's traditional ally, since Beijing was notified just 20 minutes before the test. The UN approved military and economic sanctions against the state shortly afterwards.