Inspectors from the International Atomic Energy Agency left the main site in Yongbyon north of Pyongyang after removing seals and surveillance cameras, a diplomat close to the U.N. agency said Wednesday. He spoke on condition of anonymity because he was not authorized to release the information.
They arrived in Beijing on a flight Thursday from Pyongyang, but declined to speak to reporters.
Four U.S. experts monitoring the nuclear plant in Yongbyon also were preparing to depart after North Korea ordered them out, the State Department said.
The expulsions come after the Security Council unanimously condemned North Korea's April 5 rocket launch as a violation of previous resolutions barring the North from ballistic missile-related activity. The U.S., Japan and other nations have accused North Korea of using the launch to test long-range missile technology since the delivery systems for sending satellites and missiles are similar.
North Korea, which claims the right to develop a space program, said it launched a satellite into orbit and reacted furiously to the U.N. censure by vowing to boycott international disarmament talks and restart its nuclear program.
Pyongyang conducted a nuclear test in 2006 but later agreed to dismantle its nuclear program in return for shipments of fuel oil under a 2007 deal reached with China, Russia, South Korea, the U.S. and Japan. The process has been stalled since last year by a dispute over how to verify North Korea's past nuclear activities.
North Koreans, meanwhile, were basking in a two-day holiday celebrating the April 15 birthday of late founder Kim Il Sung.
Kim and his son, current leader Kim Jong Il, are the focus of an intense personality cult in the nation of 24 million people.
APTN in Pyongyang broadcast footage of Kim Jong Il making a rare public appearance for the holiday by joining North Koreans for a celebratory display of fireworks Tuesday night on the eve of his father's birthday.
Kim waved to the crowd of cheering citizens gathered for the fireworks in central Pyongyang.
Kim, 67, made no major public appearance for months after reportedly suffering a stroke last August. He presided over the first session of the new parliament last week — his first state event since last year — in a closely watched appearance.
In addition to the U.N. inspectors, a small group of six to eight U.S. experts have been rotating into Yongbyon since November 2007.
U.S. State Department spokesman Robert Wood said their departure would be "a step backward."
"The North is going to have to deal with the consequences of such decisions. And they just bring upon themselves further isolation from the international community," he said in Washington on Wednesday.
The U.S., Japan and other participants in the nuclear talks urged the North to return to the negotiating table.
Russia's chief nuclear envoy, Deputy Foreign Minister Alexei Borodavkin, said the "most important task" now is to resume the talks — not imposing heavier sanctions on North Korea for the rocket launch, according to the ITAR-Tass news agency.