United Nations nuclear inspectors, after years of being banned from North Korea, have arrived in the North to verify the shutdown of Pyongyang's main nuclear facility. The shutdown appears to be imminent. The inspectors' visit coincides with the arrival in the North of a preliminary shipment of fuel oil from South Korea, and comes just days before six-nation negotiations on Pyongyang's overall nuclear programs are due to resume. Daniel Schearf reports from Beijing.

The team from the U.N.'s International Atomic Energy Agency left Beijing Saturday morning en route to North Korea's nuclear reactor in Yongbyon.

The inspectors' assignment is to verify Pyongyang's shutting down of the reactor. The shutdown is part of a broad agreement aimed at eventually ending North Korea's nuclear programs completely.

A U.S. official was quoted in Tokyo Saturday as saying the shutdown could come within the next several days.

A South Korean ship arrived in North Korea earlier Saturday, just ahead of the inspectors' departure, to deliver 6,200 tons of heavy fuel oil. Pyongyang had said it would not begin the shutdown until it received at least part of the 50,000 tons of energy aid it was promised under a February agreement with the South Korea, the United States, China, Japan, and Russia.

This is first time the North has allowed U.N. inspectors into the country since expelling them in late 2002, after Washington accused Pyongyang of having a secret uranium enrichment program.

IAEA officials have expressed optimism that North Korea will now go through with its promise to shut the reactor and allow the U.N. team to do its job.

Adel Tolba, the group leader, spoke to reporters Saturday before the team left Beijing.

"We are in [on] the road to Yongbyon facilities," said Tolba. "We will have our equipment with us. We will resume our work when we arrive."

North Korea is believed to have used the Yongbyon reactor to produce enough plutonium for five or more nuclear bombs, and the country set off alarm bells when it successfully tested one bomb in October last year.

The plutonium-based program, which Pyongyang acknowledges, is separate from the uranium enrichment program that Washington alleges Pyongyang is carrying out secretly.

The stop-and-start six-nation negotiations aimed at ending North Korea's nuclear programs completely are set to resume Wednesday in Beijing after months of inactivity.

In the February agreement, North Korea agreed in principle to provide full details of those programs, and eventually to abandon them in return for donations of fuel oil, food and fertilizer, security guarantees, and eventual normalized diplomatic relations with the U.S. and Japan.

The chief U.S. negotiator, Assistant Secretary of State Christopher Hill, told reporters in Tokyo that the shutdown of the reactor is expected no later than Monday.

"We understood [it would be] this weekend," he said. "I don't know whether it's Saturday, Sunday or Monday. I do know it's very soon."

He has said he would like to Pyongyang provide the details of its nuclear programs "within months," and permanently dismantle the Yongbyon reactor by the end of the year.