President Barack Obama accused North Korea of threatening the peace and security of the world by carrying out a nuclear test this morning, and demanded that it abandon its nuclear programme and return to disarmament negotiations.
"North Korea’s attempts to develop nuclear weapons, as well as its ballistic missile programme, constitute a threat to international peace and security," he said, a few hours after the underground nuclear test, which shook the earth as far away as China and was detected by earthquake monitoring equipment across the Pacific.
Mr Obama added: "By acting in blatant defiance of the United Nations Security Council, North Korea is directly and recklessly challenging the international community. North Korea’s behaviour increases tensions and undermines stability in Northeast Asia.
"Such provocations will only serve to deepen North Korea’s isolation. It will not find international acceptance unless it abandons its pursuit of weapons of mass destruction and their means of delivery," he said.
The United Nations Security Council prepared to hold an emergency meeting in New York this evening, and governments across the world denounced the test, which comes seven weeks after North Korea launched a long range rocket over the Pacific Ocean high above Japan.
Gordon Brown denounced the test as a "danger to the world" that will undermine peace prospects on the Korean peninsula.
"I condemn North Korea’s nuclear test in the strongest terms as erroneous, misguided and a danger to the world," the Prime Minister said in a statement.
"This act will undermine prospects for peace on the Korean peninsula and will do nothing for North Korea’s security," he said.
"The international community will treat North Korea as a partner if it behaves responsibly. If it does not, then it can expect only renewed isolation," he added.
A few hours after this morning’s nuclear test, the North Korea military test fired a short range missile from the same launch site.
"The Democratic People’s Republic of Korea successfully conducted one more underground nuclear test on 25 May as part of the measures to bolster up its nuclear deterrent for self-defence in every way as requested by its scientists and technicians," the state controlled Korean Central News Agency reported this morning.
The North’s first nuclear test took place in October 2006, but was judged by foreign governments to have only partially exploded. Seismic reading of the blast, and the North’s own propaganda, suggest that this one was a fuller and more powerful explosion.
"The current nuclear test was safely conducted on a new higher level in terms of its explosive power and technology of its control," KCNA added.
"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 test will contribute to defending the sovereignty of the country and the nation and socialism and ensuring peace and security on the Korean Peninsula and the region around it with the might of Songun [the "military-first" policy]."
The Japan Meteorological Agency measured seismic activity at a magnitude of 5.3 on the Richter scale, and the US Geological Survey detected a 4.7-magnitude earthquake 375 kilometres (230 miles) northeast of the North Korean capital, Pyongyang, at 9.54 am local time (1.54am British Summer Time). The 2006 test registered a magnitude of just 3.6.
Shares on South Korea’s stock exchange fell by as much as 4 percent, and the Korean won lost 1 percent of its value against the dollar after news of the test.
At Japan’s request, the UNSC will meet this evening, and no doubt hear demands for tougher retaliatory action against Pyongyang.
There was a similar outcry after the rocket launch in April. North Korea, however, insisted that rather than a missile, it was a vehicle for putting a communications satellite into orbit.
Russia and China vetoed a punitive resolution in the Security Council, but supported a chairman’s statement condemning North Korea.
The demands for action will be all the more intense this time around because of the increased seriousness of the situation.
Until the second half of last year, foreign governments assumed that, despite possessing between six and 12 nuclear warheads, North Korea lacked the capacity to miniaturise them sufficiently to mount them on a missile.
In the past few months though there have been clear signs that North Korea has become a fully fledged nuclear power, with the capacity to wipe out entire cities in Japan and South Korea.
The new reality has been spelled out by increasing numbers of authoritative experts from the head of the International Atomic Energy Agency to the US Defence Secretary.
According to intelligence briefings shown to academic experts, North Korea has successfully miniaturised nuclear warheads to the extent that they can be launched on medium-range missiles.
This puts it ahead of Iran in the race for nuclear attack capability, and seriously alters the balance of power between North Korea’s large but poorly equipped military and the South Korean and US forces ranged against it.