North Korea ? The top U.S. envoy on North Korea made a rare visit to the communist country today to inspect work to disable its nuclear complex so that Pyongyang will no longer be able to produce atomic bombs.

North Korea began disabling its plutonium-producing reactor and other related facilities last month under the guidance of U.S. experts, a key milestone in international diplomacy aimed at persuading Pyongyang to abandon its nuclear ambitions in return for economic aid and other benefits.

U.S. Assistant Secretary of State Christopher Hill is the highest-level U.S. official to check on the disablement at the North’s nuclear plant in Yongbyon, north of Pyongyang. He arrived in North Korea for a three-day trip.

North Korea had promised to complete the disabling measures by year’s end, but lead South Korean nuclear envoy Chun Yung-woo said last week it could take longer to remove about 8,000 spent fuel rods from the reactor due to technical reasons.