U.S. monitors of North Korea's nuclear program pulled out of the communist nation Friday after the regime expelled them and vowed to restart its reactor in anger over U.N. criticism of its recent rocket launch.

The four Americans arrived in Beijing on a flight from Pyongyang, but declined to speak to reporters. Their departure came a day after U.N. nuclear inspectors left the North after also being ordered out.

The exits by all international inspectors leaves the global community with no onsite means to monitor North Korea's nuclear facilities, which can yield weapons-grade plutonium if restarted.

North Korea said earlier this week it would kick out all international inspectors, restart its nuclear program and quit six-nation disarmament talks because the U.N. Security Council criticized its April 5 rocket launch as a violation of resolutions barring it from ballistic missile-related activity.

Pyongyang says the liftoff was a peaceful satellite launch, but other nations believe it was a test of its missile technology.

The North's angry reaction threw prospects for the already-stalled disarmament talks into further doubt. The U.S., China, Japan and South Korea and Russia have urged the North to return to the negotiating table, but it has not responded.

Russia's Foreign Minister Sergey Lavrov plans to visit North Korea next week, a duty officer at the Foreign Ministry in Moscow confirmed, saying more information about the trip will be released Monday. The officer spoke on condition of anonymity in line with policy.

South Korea's Chosun Ilbo newspaper reported Friday that Lavrov plans to visit Pyongyang around April 24 and is likely to meet with North Korean leader Kim Jong Il and deliver a letter from Russian President Dmitri Medvedev. The newspaper cited unidentified Russian officials.

Chinese Foreign Minister Yang Jiechi said Beijing will work to continue the six-nation disarmament talks and "hopes for the development of and improvement in relations between the United States and North Korea," according to an interview in Japan's Nihon Keizai newspaper.

China is North Korea's only major ally but backed the U.N. rebuke. In his interview, Yang did not appear to directly criticize North Korea over the launch, but said it should offer an explanation.

"North Korea announced a satellite launch," he said. "It is appropriate for North Korea to explain why it took the action."

Separately, Kyodo News agency reported that the U.S. won't pursue direct talks with North Korea at the expense of the six-party talks.

Deputy Secretary of State James Steinberg made the comment Thursday to Seiji Maehara, a top official in Japan's main opposition Democratic Party, Kyodo reported from Washington.

Steinberg also told Maehara that the U.S. will call for talks with China, Japan, Russia and South Korea by the end of this month on how to deal with North Korea, it said.

Inspectors from the International Atomic Energy Agency left North Korea on Thursday after removing all seals and switching off surveillance cameras, the IAEA said.

North Korea conducted a nuclear test in 2006 but later agreed to dismantle its nuclear program in return for shipments of fuel oil under a 2007 six-nation deal. The process has been stalled since last year by a dispute over how to verify North Korea's past nuclear activities.