North Korea says it will not participate in six-way nuclear talks unless the truth about South Korea's past nuclear activities is fully unearthed.

A North Korean Foreign Ministry spokesman said Thursday that Pyongyang has no plans to return to the negotiating table on its nuclear issue unless details of secret nuclear experiments by South Korean scientists in the 1980s and 2000 are thoroughly probed. The spokesman made the remarks during an interview with the North's official KCNA News Agency on Thursday.

The ministry spokesman said Pyongyang wants to continue the six-nation nuclear dialogue, but added that Washington's supposed 'hostile' policy toward the North and Seoul's recent nuclear revelations are hampering efforts to open the multilateral talks.

In Washington, the U.S. government rebutted Pyongyang's statement. State Department spokesman Richard Boucher insisted that the opening of a fresh round of six-way nuclear talks and investigations into Seoul's past nuclear experiments were two separate matters.

Boucher urged the North to return to the negotiating table as it had promised to at the last round of discussions, adding that all the other parties are ready and willing to hold the talks this month.