A Japanese daily says North Korea's top nuclear negotiator has hinted that uranium is not subject to its nuclear program disclosure.

The Tokyo Shimbun quoted Chinese officials as saying North Korean Vice Foreign Minister Kim Kye-gwan told his Beijing counterpart Wu Dawei that plutonium is the key to the disclosure.

The report said the comment reflects Pyongyang's intent to limit its disclosure to the production and use of plutonium.

The paper also predicted considerable difficulty in the "complete declaration" of North Korea's nuclear program as requested by the parties to the six-way nuclear talks.

China is working to hold the talks or a chief delegates' meeting at an early date, Kim, however, said the North will not join the talks for the time being, calling them premature.