North Korea will consider any U.N. economic sanctions imposed against it to be an act of war, that nation's ambassador to the United Nations said Friday.

"We consider now any kind of economic sanctions to be taken by the Security Council as a declaration of war," Pak Gil Yon told reporters at a rare news conference called to clarify North Korea's announcement earlier in the morning that it is pulling out of the Nuclear Nonproliferation Treaty.

In announcing its withdrawal from the international agreement, Pyongyang warned that any American action against it "would lead to the Third World War" and boasted it could match the U.S. in a "fire-to-fire standoff."

North Korea then added that it would be willing to talk to Washington in an effort to defuse the escalating crisis. The South Korean government called the issue a matter of "life and death."

Pak told reporters the U.S. has a "hostile policy" toward North Korea and is wrecking prospects for peace and security on the Korean Peninsula.

He said North Korea's withdrawal from the Nonproliferation Treaty was an act of self-defense against America's effort to "stifle" his country, and added that the North's disputed nuclear program has been used only for "peaceful purposes."

He also accused the U.N.'s nuclear agency of branding North Korea as a "criminal," and said the agency serves the United States' interests.

Vice President Dick Cheney, speaking to business leaders in Washington, said North Korea's decision to pull out of the agreement was a "serious concern" to the international community.

"While not unexpected, given North Korea's recent behavior, today's announcement is of serious concern to North Korea's neighbors and to the entire international community," Cheney said.

The U.S. was not surprised by North Korea's exit from the global pact, which limits nuclear weapons to the five nations that had them when the treaty was drawn up in 1968 — the U.S., Russia, China, Britain and France.

"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."

In Santa Fe, N.M., recently inaugurated Gov. Bill Richardson met with North Korean envoys Thursday night. The White House said North Korea, not the United States, initiated the unusual diplomatic channel through Richardson, a Democrat and former Clinton administration official who twice traveled to Pyongyang.

"The talks were cordial but candid," said Richardson's spokesman Billy Sparks .

The U.S. believes the North already has one or two nuclear bombs. American intelligence's recent discovery that Pyongyang had secretly revived its nuclear program led to the collapse of a 1994 agreement that sought to limit its atomic ambitions.

Retired Gen. Brent Scowcroft, who was national security adviser to the first President Bush, said he thought Pyongyang's decision to renounce the nonproliferation treaty was "more symbolic than it is changing a fundamental situation."

"They sort of forecast that when they asked the [U.N.] inspectors to leave," Scowcroft said Friday on ABC's Good Morning America. But he added that "it is a step toward keeping the tension up and trying to improve their leverage."

In Beijing, the government's official Xinhua news agency said China wanted to see a peaceful resolution to the dispute.

"We are concerned about the DPRK's announcement to withdraw from the treaty, as well as consequences possibly caused by the withdrawal," Foreign Ministry spokeswoman Zhang Qiyue was quoted as saying, referring to the North by the initials of its formal name — the Democratic People's Republic of Korea.

Australia, Japan, the Philippines and Russia were among countries that expressed deep concern. Britain condemned the North Korean move as "a wrong decision."

The treaty says a nation that withdraws from the pact must give notification three months in advance. North Korea, however, said it was withdrawing as of Saturday.

Only four countries — Cuba, India, Israel and Pakistan — have not signed the nonproliferation treaty.

India and Pakistan are engaged in a regional nuclear arms race, and Israel's nuclear arsenal, though never confirmed, is assumed to have existed for as long as 30 years. Cuba is a member of a treaty establishing a nuclear-free zone in Latin America.

North Korea said it had quit the treaty because of alleged U.S. aggression, but said it had no intention of producing nuclear weapons and would use its nuclear program only for peaceful purposes "at this stage."

The declaration heightened tension as the United States and its allies seek a diplomatic solution, although Pyongyang's action could mean that it is trying to pressure the United States into making concessions. North Korea wants Washington to sign a nonaggression treaty and give it economic aid.

South Korean President Kim Dae-jung said dialogue was the only way to solve the nuclear crisis, which he called a matter of "life and death."

His National Security Council held an emergency meeting. Afterward, the Foreign Ministry said the North's withdrawal was a "serious threat to peace and stability on the Korean Peninsula" and urged it to retract its decision.

The nuclear tension could be discussed at Cabinet-level talks between the two Koreas that are scheduled for Jan. 21-24 in Seoul. However, North Korea says the issue is strictly a matter between it and the United States.

In a clear signal it feared losing face, Pyongyang said through its official Korean Central News Agency, "We can no longer remain bound to the NPT, allowing the country's security and the dignity of our nation to be infringed upon."

"Though we pull out of the NPT, we have no intention of producing nuclear weapons and our nuclear activities at this stage will be confined only to peaceful purposes such as the production of electricity," it continued.

However, analysts say a nuclear reactor in the North Korean town of Yongbyon — the focus of the latest dispute — provides a negligible amount of power. The facility was the centerpiece of a weapons program until it was frozen in a 1994 energy deal with the United States.

U.S. officials said that North Korean negotiators acknowledged in October that they had a second, clandestine nuclear program.

In 1993, North Korea also announced that it was withdrawing from the treaty, but suspended the decision three months later and entered talks with the United States. It again left open the possibility of a negotiated solution.

"If the U.S. drops its hostile policy to stifle the DPRK and stops its nuclear threat to it, the DPRK may prove through a separate verification between the DPRK and the U.S. that it does not make any nuclear weapons," the North Korean government statement said.

However, the North's defiant posture raises the possibility that the International Atomic Energy Agency will send the matter to the U.N. Security Council, which could choose to impose economic sanctions. Such a step could lead to more defiance from the isolated North.

The crisis worsened last month when Pyongyang expelled U.N. inspectors at the Yongbyon site and said it was reactivating the facilities. Experts say North Korea could make several more bombs within six months if it extracts weapons-grade plutonium from spent fuel rods.

North Korea joined the Nuclear Nonproliferation Treaty in 1985. In 1994, North Korea agreed to freeze its nuclear facilities at Yongbyon under an energy deal with the United States. Those facilities are the focus of the new crisis.

A U.N. relief official, meanwhile, appealed for more food aid for North Korea as part of the World Food Program's plans to feed 6.5 million North Koreans this year, said Richard Corsino, the WFP's director for North Korea. The isolated, Stalinist dictatorship has relied on foreign food aid since the mid-1990s.

"We don't have enough contributions at this point to give us any degree of confidence that we will be able to meet our targets for the first half of this year," said Corsino, who stopped in Beijing after a visit to WFP headquarters in Rome.

The Associated Press contributed to this report.