US monitors of North Korea's nuclear program left the communist nation Friday after the regime ordered them out and vowed to restart its reactor in anger over UN 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 UN nuclear inspectors left the North. The pullout of 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 vowed earlier this week to restart its nuclear program and quit six-nation disarmament talks because the UN Security Council criticized its April 5 rocket launch as a violation of resolutions barring it from ballistic missile-related activity.