BBC correspondents report from around the world following North Korea's announcement that it has carried out a nuclear test.
FRANCES HARRISON, TEHRAN
State run Iranian television has gone into huge detail about the achievements of the North Koreans, producing maps and diagrams.
The tone is clearly congratulatory and there's considerable excitement.
An expert interviewed on Iranian television gave his version of the history of North Korea's nuclear talks with the international community.
He spoke of America's failure to give security guarantees to North Korea and deliver on its promise of a lightwater reactor and nuclear fuel.
This, the expert said, had forced the North Koreans to develop a nuclear weapon and he warned that other countries might follow the North Korean model and join the nuclear club.
It's hard to imagine what other countries are being referred to, except Iran.
And the parallels are clear: Europe offered Iran lightwater reactors and nuclear fuel in return for suspension of its own enrichment programme. But Iran rejected the offer.
What's not clear in Tehran yet is whether or not the North Korean test will harden international opinion against Iran's nuclear programme at a time when UN sanctions are being seriously considered.
RUPERT WINGFIELD-HAYES, BEIJING
Using very undiplomatic language, China's foreign ministry denounced the test as brazen and demanded the North Koreans take no further action to worsen the situation.
The test has shattered China's decade-long effort to use diplomacy to halt North Korea's nuclear programme.
Beijing will now come under tremendous pressure from the US and Japan to support much tougher sanctions against Pyongyang.
But that is something China will still be loathe to do.
Beijing's number one priority remains the survival of the regime in Pyongyang. From China's point of view a nuclear-armed North Korea is still better than no North Korea at all.
RICHARD GALPIN, MOSCOW
The Russian defence ministry confirmed the test. A top military officer said monitoring systems had detected an explosion in North Korea early on Monday morning. He said it was 100% it was an underground nuclear explosion.
Moscow has close relations with Pyongyang and maintains an embassy there.
Last week, Russian Foreign Minister Sergei Lavrov announced his government was in direct contact with the North Korean authorities and was trying to persuade them not to go ahead with a test.
But clearly that diplomatic effort, like that of the rest of the international community, failed.
So far there has been no official response from the Russian foreign ministry but the issue now is whether Moscow will support calls already coming from the US for a tough response from the UN Security Council.
SARAH MORRIS, WASHINGTON
Reports that North Korea conducted a successful nuclear bomb test met with strong condemnation from the White House.
A simple statement said that such a test would constitute a provocative act in defiance of the international community.
The administration has always made it clear that a North Korea armed with nuclear weapons was unacceptable and it imposed financial sanctions on the country nine months ago.
The White House spokesman said that it was hoped the UN Security Council would take immediate actions to respond to this unprovoked act and that the US was closely monitoring the situation. He said the test could aggravate tensions in north-east Asia.
LEO LEWIS, TOKYO
Japanese Prime Minister Shinzo Abe, visiting Seoul for a summit meeting with his South Korean counterpart, said that reports that Pyongyang had conducted a nuclear test were absolutely unacceptable.
Mr Abe added that the crisis should be approached in a cool-headed manner, stressing the importance of maintaining close relations between Japan and South Korea.
Japan's chief government spokesman Yasuhisa Shiozaki said that if indeed North Korea's nuclear test did take place as claimed, it represented a serious threat.
Foreign Minister Taro Aso said that a new UN Security Council resolution against North Korea was now possible.
Shortly after North Korea claimed success in its nuclear test, the Japanese government set up a task force within the prime minister's office to deal with the issue.
Japan has already said it will work closely with the US, China and South Korea to resolve the crisis.
CHARLES SCANLON, SEOUL
South Korean President Roh Moo-hyun described the test as a grave threat to peace, and he promised a stern response.
The South Korean army was placed on a higher state of alert shortly after the explosion was detected in a mountainous area about 120km (75 miles) from the Chinese border.
A South Korean spokesman said it measured about 3.5 on the Richter Scale, about the same as a small to moderate earthquake.
South Korea and Japan have said they will not tolerate a nuclear North Korea.
JILL MCGIVERING, LONDON
South Korea has responded to news of the test by announcing it is suspending a shipment of emergency aid.
The cancelled shipment was part of an emergency package - a specific response to the floods in July.
South Korea had already suspended its main programme of food aid after North Korea's last missile tests, also in July.
The World Food Programme, which was forced last year to reduce its own aid to North Korea, is already raising concerns that political reaction to Pyongyang's move could further compromise its ability to feed the country's most vulnerable people.
NICK BRYANT, SYDNEY
Australian Prime Minister John Howard was one of the first to condemn the nuclear test by North Korea, which he said had been confirmed by seismic measurements.
He said Australia would be calling for sanctions at the UN and that the country was disturbed and outraged by the test.
The Australian government has adopted a consistently tough stance against Pyongyang, not just because of its steadfast support for the us but out of concern that it could one day be targeted by North Korean weapons.
Australia is one of the few countries to have diplomatic ties with the communist state and has been a key intermediary in efforts to resolve the nuclear crisis.
ANDREW WALKER, ECONOMICS CORRESPONDENT, LONDON
Financial markets have been affected by the news of the nuclear test.
Share prices have fallen in most markets, and the South Korean and Japanese currencies also dropped. But the scale of financial market reaction was for the most part moderate.
It reflects the fact that the test was not a complete surprise.
There is however some rather non-specific unease about how events might unfold; that perhaps sanctions or political instability in North Korea might disrupt economic activity in South Korea, China or elsewhere.