The six nations negotiating the North Korean (searchnuclear standoff will hold low-level meetings on May 12 in Beijing to lay the groundwork for the next round of talks, South Korea (searchand China (search) said Thursday.

The apparent breakthrough comes as the United States reportedly prepares to upgrade its estimate of North Korea's nuclear arsenal to at least eight atomic weapons (search), from its long-standing estimate of "possibly two."

The report, disputed by Seoul, is being prepared by U.S. intelligence officials to account for strides North Korea has made since last year, when it restarted its nuclear reactor and plutonium reprocessing facility in Yongbyon, the Washington Post reported Wednesday, citing unnamed officials involved in the estimate overhaul.

The officials have also concluded that a separate uranium-based nuclear program will be operational by 2007, producing enough material for as many as six additional weapons a year, the report said.

An upgrade would be seen as upping pressure on other participants in the six-nation negotiations to back Washington at the table. U.S. State Department spokesman Adam Ereli called the report "speculative."

In Seoul, South Korean Deputy Foreign Minister Lee Soo-hyuck quoted U.S. authorities as saying that the Washington Post report was "groundless."

Lee said that an estimate of eight nuclear bombs is based on the assumption that the communist state has reprocessed all its 8,000 spent nuclear fuel rods.

The rods, if chemically treated, can yield enough plutonium for several bombs. North Korea says it has reprocessed all and is already increasing its "nuclear deterrent." Speaking at a news conference, Lee said: "There is no scientific proof that the North has reprocessed all the 8,000 rods."

South Korea believes the rival North has enough nuclear material to build one or two nuclear bombs.

Lee said that the six nations involved in resolving the dispute — the United States, China, the two Koreas, Russia and Japan — are scheduled to begin working level talks May 12 in the Chinese capital.

In Beijing, Chinese Foreign Ministry spokesman Kong Quan said the "fundamental goal" of the so-called working-group meetings was to prepare for a third round of six-party talks to be held by the end of June.

Lee said South Korea, the United States and Japan would consider giving the North energy aid if it freezes all its nuclear facilities, including those for power generation, with the condition that it will eventually completely dismantle them.

"As we go into these talks, our principal position remains the same and unchanged, that North Korea should dismantle its nuclear facilities completely and that we cannot tolerate North Korea possessing nuclear weapons," Lee said.

The nuclear standoff began in October 2002, when U.S. officials said North Korea admitted having a secret nuclear program in violation of a 1994 pact.

North Korea says it will dismantle its nuclear weapons facilities only if the United States provides economic aid and makes a nonaggression pledge. The United States demands that North Korea first scrap all its nuclear facilities.