Former Clinton official and New Mexico Gov. Bill Richardson is being tapped by the White House to help broker talks between North Korea and the U.S. in an increasingly tense nuclear arms situation, Bush administration officials confirmed Thursday.

Tensions escalated late Thursday when North Korea's official news agency announced the nation's withdrawal from the global nuclear arms control treaty.

North Korea claimed that leaving the Nuclear Nonproliferation Treaty will free it from safeguard obligations to the U.N. International Atomic Energy Agency. "The withdrawal from the NPT is a legitimate self-defensive measure taken against the U.S. moves to stifle" North Korea, its official news agency said. North Korea has repeatedly accused the United States of plotting to invade it.

The announcement came as the United States was awaiting a reply from Pyongyang about its decision to open dialogue to seek a peaceful resolution of the country's nuclear weapons development. The State Department and White House had no immediate comment on the withdrawal.

While Richardson met with the envoys, the administration appeared to expand on its demands. Officials said that even if talks resumed, North Korea must do more than stop its efforts to produce plutonium and enrich uranium.

"The next step is for North Korea to completely dismantle its nuclear weapons program," said Sean McCormack, a White House spokesman. Separately, a senior administration official said the White House wants North Korea's nuclear facilities at Yongbyon taken apart.

The White House said North Korea, not the United States, initiated the unusual diplomatic channel through Richardson, a Democrat and former Clinton administration official.

"The only message we expect is what America's position is, that we are ready to talk, and that we will not negotiate," presidential spokesman Ari Fleischer said. "That's the U.S. position. You should not see this as anything beyond that."

Richardson walked the two officials out of the governor's mansion after two hours of what Richardson's spokesman described as a working dinner. The North Koreans left in a white sports utility vehicle. Neither side commented to reporters. They were to meet again Friday.

"I want to be able to help my country," Richardson, who was sworn in Jan. 1 as governor, said earlier. He had visited North Korea on two diplomatic missions while he was still a member of Congress during the 1990s.

The initiative for the meeting was taken by North Korea's deputy U.N. ambassador, Han Song Ryol. It came after meetings held Monday and Tuesday among U.S., South Korean and Japanese officials on the North Korean nuclear situation.

The United States offered in a joint statement to hold talks with North Korea on the dispute over its resumption of a nuclear weapons program.

North Korean diplomats require U.S. permission to leave New York City, and Secretary of State Colin Powell granted it on Wednesday to facilitate the talks in Santa Fe, N.M. A second diplomat, Mun Jong Chol, was joining Han.

Richardson said before the meeting: "I support the administration's policy. I am going to try to be helpful. I am not an official negotiator. The administration has many channels that they are pursuing with the North Koreans."

State Department spokesman Richard Boucher said Powell went over U.S. policy toward North Korea with Richardson. The governor has had previous contacts with Han.

For Richardson, the role of diplomatic troubleshooter is not new.

In 1996, as a New Mexico congressman, he went to North Korea and helped secure the release of an American who was detained for three months on spy charges. In 1994, he helped arrange the freedom of a U.S. soldier whose helicopter had strayed into North Korea.

He also undertook diplomatic forays into Sudan, Cuba and Iraq during his House days. He was sometimes known at the "U.S. ambassador to rogue states."

He served both as U.N. ambassador and energy secretary for the Clinton administration. North Korea may have turned to him after recalling the warmer ties it enjoyed with Washington during that period.

North Korea welcomed former Secretary of State Madeleine Albright to its capital, Pyongyang, in October 2000. Bill Clinton considered a visit in the final weeks of his presidency but decided against it. Just a year after Clinton left office, President Bush designated North Korea as part of an "axis of evil."

The Bush administration contends that North Korea acted in bad faith during the Clinton era by carrying out a secret nuclear weapons program in violation of agreements even as it was displaying friendship toward Washington.

At the State Department, Boucher said the United States is insisting that North Korea "promptly and verifiably" dismantle its nuclear weapons programs.

The Bush administration has been hoping international pressure on North Korea will force it to reconsider its nuclear program.

North Korea appears to have scant support from the outside world but the U.S. ambassador to Russia, Alexander Vershbow, told reporters in Washington on Thursday that Russia was not doing enough to influence the isolated nation.

Russia could offer to help North Korea with its energy needs, Vershbow said in remarks at the Carnegie Endowment for International Peace, a Washington research group.

Fox News' Wendell Goler and Teri Schultz and The Associated Press contributed to this report.