A U.S. diplomat who returned from a visit to North Korea has briefed South Korean officials on his trip to the communist country.

Sung Kim met with Korean officials in Seoul and explained the progress in the North's disablement of its nuclear facilities and declaration of its nuclear programs.

Kim, head of the State Department's Korea Desk, visited Pyongyang for three days from Wednesday.

During his talks with North Korean officials, the diplomat urged the North to declare a suspected uranium enrichment program and an alleged transfer of nuclear materials to Syria.

A diplomatic source in Seoul quoted Kim as saying that the North's nuclear disablement was progressing smoothly.

On the declaration of its nuclear programs, the North reportedly plans to provide a list of declarations to the United States soon. The United States wants the North to make a full and complete declaration of all its nuclear programs, including the suspected uranium enrichment program.

Kim arrived in Seoul amid a news report that uranium traces were found on aluminum tubes North Korea provided to the United States. But the diplomatic source said the matter was not discussed in his talks with South Korean officials.

North Korea has denied the U.S. allegation that it had a clandestine nuclear weapons program based on enriched uranium.

Kim came to Seoul Friday afternoon through the border village of Panmunjeom. He is scheduled to return to Washington Sunday.