The US envoy to North Korea would return from Pyongyang with a 'significant number' of documents detailing the communist country's nuclear programme, the US State Department said Thursday.

Sung Kim, director of the State Department's Korea office, led a US delegation earlier Thursday to North Korea - the second US visit in three weeks - as part of a diplomatic push for North Korea to dismantle its nuclear weapons programme. Sung was expected to return Friday to South Korea.

'I know that he is going to bring with him a significant number of documents related to North Korea's plutonium programme. And we'll have an opportunity over the coming days and weeks to assess the significance of these documents,' State Department spokesman Sean McCormack said.

McCormack could not say whether the new documents amounted to a full declaration by the North Koreans of their nuclear activities. He said a declaration would also likely be made to China, which chairs the six-party talks.

North Korea must provide a full declaration before the six-way talks - involving the two Koreas, the US, Japan, China and Russia - can resume after being suspended for months.

Washington has pressured North Korea to declare all nuclear activities and end nuclear proliferation under a disarmament agreement reached in February 2007.

'Our top three priorities are going to be verification, verification, verification,' McCormack said of the new documents.

Pyongyang did submit limited details of its nuclear weapons programmes to the US late last year. The US also wants North Korea to acknowledge concerns about its role in helping Syria build a clandestine nuclear weapons facility.

The US last month accused Syria of building a secret reactor with North Korean technical help, a charge denied by both countries. The alleged facility was the target of an Israeli air raid in September, the White House said.