Pyongyang, which has raised the stakes in the crisis with claims it was making atomic bombs after reprocessing spent fuel rods, said it "would not allow Japan to participate in any form of negotiations for the settlement of the nuclear issue in the future."

The statement cast doubt on plans for a new round of talks, which South Korean President Roh Moo-Hyun said Tuesday would take place soon.

A first round of talks in Beijing in August ended inconclusively and the North Koreans expressed no interest in continuing the dialogue without concessions from the United States, which Washington refused.

Pyongyang has held out for a non-aggression pact as a first step before responding to Washington's demand for a complete and verifiable dismantling of its nuclear weapons drive.

The North's official Korean Central News Agency (KCNA) said Tuesday it would step up its nuclear weapons drive and dismissed as a "blank sheet of paper" an offer tendered by the top US envoy for Asia, James Kelly, of a non-binding written security guarantee.

"The DPRK stand on this matter is that ... written security assurances are nothing but a blank sheet of paper which can never give any legal guarantee that the Bush administration will not attack the DPRK," the statement monitored here said.

North Korea has accused Washington of planning a nuclear strike against it, ignoring frequent denials from US officials including President George W. Bush and Kelly, the assistant secretary of state for East Asian and Pacific Affairs.

Meanwhile, in demanding Japan be denied a seat at any further multilateral discussions of its nuclear ambitions, Pyongyang criticized Tokyo for aligning itself with Washington on the nuclear crisis and for its crack-down on a pro-North Korean group of ethnic Korean residents in Japan known as Chongryon.

It also faulted Tokyo for using the talks to raise the issue of Japanese citizens abducted by North Korea during the 1970s and 1980s.

Japan rejected North Korea's attempt to exclude it from the next round of talks that also include Russia, South Korea, China and the United States, saying Pyongyang had no authority to do so.

"We have no intention of accepting it at all," Japanese Foreign Ministry spokesman Hatsuhisa Takashima said in Tokyo.

"The North Korean nuclear issue is not a bilateral issue between Japan and North Korea ... but it is something the international community should discuss together."

Tension between Pyongyang and Tokyo has risen steadily since September last year, despite a landmark summit between Japanese Prime Minister Junichiro Koizumi and North Korean leader Kim Jong-Il that initially offered hope of improved ties.

Kim's admission that North Korea had kidnapped 13 Japanese citizens in the 1970s and 1980s caused an outcry in Japan that was further fueled by the return of five abductees in October last year for their first visit home in more than two decades.

South Korea's Roh was optimistic earlier Tuesday that "good results" would come from any further round of multilateral talks, but a South Korean foreign ministry official later acknowledged the negative impact of the latest statements from the North.

"This is not a good situation," said the official who asked not to be identified.

"So far, efforts to resolve the nuclear issue have been staged under the cooperation framework of South Korea, the United States and Japan."

WAR.WIRE