Seoul - Documents that North Korea has handed over to a visiting US envoy are primarily devoted to describing the operation of three facilities at its nuclear centre in Yongbyon, South Korean officials told the national news agency Yonhap Friday.

The facilities are Yongbyon's nuclear reactor, a fuel-production plant and a fuel-reprocessing facility that recovers plutonium from spent fuel, the officials said.

North Korea handed over a "significant number" of documents related to North Korea's plutonium programme to Sung Kim, director of the US State Department's Korea office, a department spokesman said Thursday in Washington.

Kim led a US delegation into North Korea Thursday for the second US visit in three weeks as part of a diplomatic push for North Korea to dismantle its nuclear weapons programme. He was expected to return Saturday to South Korea, the US embassy in Seoul said, and would bring the documents with him on his return to Washington.

State Department spokesman Sean McCormack said US officials would assess the significance of the documents over the coming days and weeks and could not yet say whether they amounted to a full declaration by the North Koreans of their nuclear activities.

Six-nation talks on ending Pyongyang's nuclear programmes have been stalled for months over whether North Korea submitted a complete declaration of its nuclear facilities, activities and materials as it pledged to do so in return for aid.

Pyongyang did submit details about its nuclear weapons programmes late last year, but Washington said they were incomplete.

It said Pyongyang did not disclose a programme to enrich uranium, which can be used to build nuclear weapons, or its role in helping Syria build a clandestine nuclear-weapons facility. North Korea denied it was involved in either activity.

The six-nation talks involve the two Koreas, the United States, China, Japan and Russia. (dpa)