Faced with news that North Korea has quit the Nuclear Nonproliferation Treaty, South Korea on Friday called for dialogue with its communist rival as a matter of "life and death" while neighboring Japan demanded Pyongyang reverse its decision.
Moscow did the same and expressed "deep concern" that North Korea's move would harm global security.
Early U.S. reaction was cautious.
"This is not at all unexpected," said John Bolton, U.S. undersecretary of state for arms control, who was visiting Thailand. "The North Koreans were not adhering to the treaty when they were still a party to it."
There was no immediate comment on the spiraling crisis from China, one of the North's few friends. Australia, a close U.S. ally, said it would send a diplomatic team to Pyongyang next week.
Financial markets in South Korea and Japan reacted nervously.
North Korea announced Friday it had withdrawn from the treaty in self-defense against alleged U.S. aggression, but said it would not develop nuclear weapons "at this stage."
The 1968 nonproliferation treaty is considered a cornerstone in the effort to stop the spread of nuclear weapons.
Only four other countries — Cuba, India, Israel and Pakistan — have not signed it, though Cuba is a member of a treaty establishing a nuclear-free zone in Latin America.
In response to North Korea's decision, South Korea's government convened an emergency meeting of its security council. President Kim Dae-jung, who leaves office next month after years of trying to improve relations with the North, said talks would be key to a solution.
"The nuclear issue is tied to our life and death," Kim said, according to the Yonhap news agency. "We must have the patience to resolve the issue peacefully."
Before the North's announcement, the South's president-elect Roh Moo-hyun warned of the dangers of punishing Pyongyang over its nuclear weapons program.
The Russian Foreign Ministry said North Korea's decision "can only aggravate the already tense atmosphere around the Korean peninsula."
Russia said North Korea must "listen to the unanimous opinion of the world community," abide by its commitments to nonproliferation and enter into "equal and mutually beneficial dialogue ... in the interests of international peace and stability."
The French foreign minister, now on a visit to China, said Asia, the United States and Europe must stand together.
"France condemns North Korea's decision," Foreign Minister Dominique de Villepin said in a speech to students at Shanghai's Fudan University. "North Korea must understand that it has no other choice but to denounce its nuclear program."
In Tokyo, Japanese Chief Cabinet Secretary Yasuo Fukuda said: "Our nation will strongly demand from North Korea a quick retraction of its statement and a positive response to solving the nuclear weapons problem.
Fukuda said Japan will work closely with the United States, South Korea and other nations as well as the U.N.'s International Atomic Energy Agency to address the crisis.
Jitters over North Korea helped push down stock prices in Tokyo and the Japanese yen. The Nikkei Stock Average slid 0.32 percent, and the dollar rose 0.95 yen from a day ago.
"When you realize that Japan's the one within reach of North Korea's missiles, you don't really want to be buying the yen," said Minoru Shioiri, manager of foreign exchange at Mitsubishi Securities.
South Korea's main index dipped right after the announcement but recovered later in the day to close down 0.3 percent. Markets elsewhere in the region — Hong Kong, Sydney, Taiwan and the Philippines — shrugged the fears off and closed higher.
Australia said it will send three senior diplomats to North Korea next week to help ease the situation.
Foreign Minister Alexander Downer said Washington had been told of the plan to send the delegation, but denied the Australian trio were carrying a message at Washington's behest.
Vietnam called for restraint by all parties while the Philippines and Malaysia expressed dismay.
"We call on the DPRK to reverse its decision," Philippine Foreign Secretary Blas Ople said, using the acronym for North Korea's official name.
Malaysia said North Korea was taking a big step back.
"The Korean peninsula should be free of nuclear weapons," Foreign Minister Syed Hamid Albar told reporters. "It should not be a place for big-power rivalry."