North Korea's neighbors are scrambling to forge a common front against Pyongyang's threatened nuclear test, with South Korea warning of a regional atomic arms race that could upend the balance of power in Northeast Asia.
Cooperative efforts displayed by Japan, China and South Korea on Wednesday marked a sharp contrast with the fractured reaction to a series of North Korean missile tests in July, after which China and South Korea accused Japan of overreacting.
On Wednesday, China _ the North's main ally and key benefactor _ appealed to Pyongyang to show calm and restraint, issuing an unusually pointed statement that referred to North Korea by name instead of its usual appeals for all sides to remain calm.
Japan, China and South Korea announced a series of summit meetings over the coming week to repair damaged ties and coordinate a strategy. Japanese Prime Minister Shinzo Abe will meet with Chinese President Hu Jintao on Sunday and South Korean President Roh Moo-hyun on Monday. Roh will then visit Beijing for talks with Hu and other officials on Oct. 13.
The three countries are key players _ along with the United States and Russia _ in the long-stalled six-nation talks aimed at persuading Pyongyang to give up its nuclear ambitions in return for badly needed economic aid.
The joint effort came after communist North Korea triggered global alarm Tuesday by saying it will undertake an unprecedented nuclear test in a step toward building the atomic arsenal it views as a deterrent against any U.S. attack.
It is the first time the North has publicly announced plans to conduct a nuclear test, though recent reports have said it may be preparing one. North Korea claims to have nuclear weapons, but detonating one would be the first proof of its atomic capabilities.
U.S. Assistant Secretary of State Christopher Hill, the chief envoy to disarmament talks, said the United States has passed a message of "deep concern" through diplomatic channels at the United Nations but has yet to hear back from North Korea.
A U.S. intelligence official, speaking on condition of anonymity, said the United States is now seeing the movement of people, materials, automobiles and other activity around one possible test site, but it could be similar to the activity that was seen a couple months ago. At that time, no test occurred.
The official noted that international observers don't have a baseline for comparison, because North Korea has never performed a nuclear test.
South Korea's top official on dealings with the North, Unification Minister Lee Jong-seok, said Wednesday there were no signs of an imminent test. And Japan's Asahi newspaper reported that two Japanese spy satellites focusing on a suspected underground test site had not observed any activities apparently connected to test preparations as of Tuesday.
But Lee warned there was "a high possibility" North Korea would go ahead with one if "efforts to resume the six-party talks fail."
North Korea has boycotted the six-nation nuclear talks for nearly a year, angered by American financial restrictions imposed over the North's alleged illegal activities such as money laundering and counterfeiting.
Some experts believe the North has enough fissile material to build at least a half-dozen nuclear bombs, though there are doubts about whether it could deliver them accurately on a warhead.
Any display of Pyongyang's nuclear force could prompt Japan to go nuclear and trigger a regional arms race, South Korean Vice Foreign Minister Yu Myung-hwan warned. Speaking to lawmakers, Yu said such a North Korean nuclear test "could provide a pretext for Japan's nuclear armament."
"This will prompt countermoves by China or Russia and lead to a change in the balance of power in Northeast Asia," Yu said.
In a worst-case scenario, analysts have speculated, a test could push Japan to seek its own nuclear deterrent, intensifying historical tensions with China and South Korea, both of which suffered under Japanese colonial rule in the early 20th century.
Just last month, a think tank run by former Japanese Prime Minister Yasuhiro Nakasone proposed in a policy paper that Tokyo "consider the nuclear option."
Roh, the South Korean president, called Wednesday for a "cool-headed and stern" response to the North's announcement, while Foreign Ministry spokesman Choo Kyu-ho said a test could cause Seoul to change its engagement policy toward the communist regime.
South Korea has consistently pursued dialogue with North Korea since their leaders first met in a historic summit in 2000.