U.N. nuclear experts left North Korea on Thursday after the communist regime ordered their expulsion amid an escalating standoff over the regime's recent rocket launch.

Inspectors from the International Atomic Energy Agency left the main site in Yongbyon north of Pyongyang after removing all seals and switching off surveillance cameras, IAEA spokesman Marc Vidricaire said in a statement.

They arrived in Beijing on a flight Thursday, but declined to speak to reporters.

Four U.S. experts monitoring the nuclear plant in Yongbyon were also preparing to depart after North Korea ordered them out, the State Department said. A small group of 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 ordered the monitors out on Tuesday after the U.N. 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.

China, which is Pyongyang's only major ally but backed the U.N. rebuke, urged calm and restraint.

"We hope all parties could proceed from the long-term and overall interest, exert calmness and restraint and properly handle relevant issues so as to devote themselves to safeguarding the six-party talks," Foreign Ministry spokeswoman Jiang Yu said.

Russian special envoy Grigory Logvinov called the North's move "disappointing," but held out hope for the resumption of nuclear talks.

"We believe that there is a chance to return to the negotiating table — nobody has burned bridges and the door has not been slammed shut," Logvinov was quoted by the Interfax news agency as saying.

South Korea joined the U.S. and Japan in urging the North to return to the negotiating table. Speaking in Tokyo, South Korean Foreign Minister Yu Myung-hwan said he hoped Pyongyang would make an effort to rejoin the talks.

Russia's chief nuclear envoy, Deputy Foreign Minister Alexei Borodavkin, has getting the talks back on track is the "most important task," according to the ITAR-Tass news agency.

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.