Two inspectors from the United Nations International Atomic Energy Agency (IAEA), which has been monitoring North Korea's nuclear facilities for the past eight years, arrived in Beijing Tuesday after being expelled.

North Korea ordered the inspectors to leave the country amid an escalating standoff over its plans to revive the mothballed nuclear complex at Yongbyon, 90 kilometers (60 miles) north of Pyongyang.

As Pyongyang threw a cloak of secrecy over the nuclear plant, IAEA officials said the inspectors would submit their report on North Korea to the agency's board on January 6.

The inspectors were carrying home the IAEA's most sensitive documents and equipment used to monitor a freeze on nuclear activities at the complex under a US-North Korean accord signed in 1994.

Their departure deprives the international community of detailed information about the North's nuclear activities. Daily reports from the inspectors have kept the world abreast in recent days of the North's moves to reactivate its nuclear program.

The removal of UN surveillance in Yongbyon came as North Korea's ambassador to Moscow Pak Ui Chun said his government could no longer honour the nuclear Non-Proliferation Treaty (NPT).

"North Korea cannot currently fulfill its obligations to the Non-Proliferation Treaty and it is the fault of the United States,"

Pak was quoted as saying by Russia's Interfax news agency.

The United States is "threatening us with carrying out a preventative nuclear strike," he said.

"In these circumstances, we also cannot fulfill the Non-Proliferation Treaty, the basic obligation of which is that nuclear states do not use the nuclear weapon against states which do not possess it," he added.

Pak said Pyongyang also threatened to withdraw from the treaty in 1993, but formal withdrawl was avoided with the signing of the so-called Agreement Framework with the United States in 1994.

North Korea's move to revitalise the Yongbyon nuclear complex has triggered an angry response from the United States, which said it would pay "a serious price" in withheld international aid.

"The entire world stands ready to help North Korea, but North Korea will not realize any of the benefits and the help that they need until they reverse (their) current course," said White House spokesman Scott McClellan.

"North Korea is continuing to isolate itself," he said. "As long as they continue down their current course, North Korea will continue to pay a serious price."

The US warning, however, drew a lukewarm reaponse from South Korea, a close ally since the 1950-53 Korean War, and Russia.

Russian Foreign Minister Igor Ivanov issued Moscow's strongest condemnation yet of the former ally's nuclear program. But he insisted sanctions against Pyongyang were premature.

South Korean president-elect Roh Moo-Hyun also reinforced Seoul's rejection of US moves to punish North Korea with economic sanctions.

"It ought to be borne in mind that a failed US policy toward the North would be a matter of life and death for South Koreans while it would not be to US citizens," Roh said.

"Therefore, any US actions (toward the North) must give priority to South Korea's stance."

Washington has reportedly prepared a policy of "tailored containment" against North Korea, putting financial and political pressure on Pyongyang as the next step.

US officials downplayed an apparent rifts with South Korea and Russia over how to deal with North Korea's pursuit of nuclear weapons.

But Roh, who will take office on February 25, vowed not to blindly follow the "US lead" in averting a showdown over the North's nuclear program.

"I am skeptical about the effectiveness of the US policy of tailored containment in restraining the North or forcing it to surrender," he said.

But South Korean Defense Minister Lee Jun urged his military to maintain readiness for a possible conflict with the North.

"Whatever changes take place in inter-Korean relations, there will be no changes to the mission (the armed forces) have to perform," he said.

SPACE.WIRE