U.S. and North Korean envoys held their third one-on-one meeting Thursday, a day after the two sides staked out tough positions in talks aimed at persuading the communist North to give up nuclear ambitions.

North Korea (search) claimed in February to have nuclear weapons (search), but a news report Thursday said the reclusive nation hasn't assembled a working nuclear bomb, though it has acquired all the components necessary to build one.

A diplomatic source close to the arms talks told Russia's (search) Interfax news agency that Pyongyang informed China that February's announcement meant the North had the ability to build a detonator for an atomic bomb — the most sophisticated element of the weapons design.

North Korea has avoided spending to build up a nuclear stockpile, but the source told Interfax that the country would begin to do so in the face of unacceptable demands or a lack of security guarantees from the United States and its allies.

At the talks, U.S. Assistant Secretary of State Christopher Hill (search) and North Korean Vice Foreign Minister Kim Kye Gwan (search) met Thursday morning for two hours but no details on what they discussed were immediately available, the U.S. Embassy said.

The Americans proposed an international inspection of North Korea's nuclear facilities in September, Interfax reported, citing a North Korean source. The source said the proposal was counter to the North's principle of seeking step-by-step rewards for its pledges and actions, but declined to specify how the country would respond to the offer.

The increased contacts between the Americans and North Koreans are a change from the previous three rounds of nuclear talks, where Washington mostly shunned direct contact with the communist nation. The last round of the six-nation talks was in June 2004 and the latest began this week after the North ended a boycott over what it called "hostile" U.S. policies.

Japan's main delegate, Kenichiro Sasae, said the U.S.-North Korea talks Thursday would determine the course of the following negotiations. Without progress between those two countries, there won't be agreement on a joint statement from all sides at the conclusion of the talks, Sasae said.

That document was still under discussion Thursday afternoon and wasn't expected to be issued by the end of the day, said Chinese Foreign Ministry spokesman Qin Gang. No schedule has been set for Friday's meetings, he said.

Qin said the United States and North Korea were "in the process of finding common ground and measuring their differences."

Also Thursday, China's Foreign Ministry hosted a lunch for envoys from all six governments — China, Japan, Russia, the United States and the two Koreas — in an apparent effort to maintain a cordial tone after the often-strained atmosphere during earlier rounds.

South Korea's chief envoy to the nuclear talks said Thursday "there was no way of knowing" when the meetings would end. The sides will have to talk at least until Friday "to tell whether (the negotiations) would continue into next week," Deputy Foreign Minister Song Min-soon said.

Earlier at the talks, North Korea reportedly said the United States must abandon plans to topple its regime and establish mechanisms for peaceful coexistence.

The North also raised the issue of what it claims is a U.S. nuclear arsenal that could be used against the North, a senior American official said on condition of anonymity because the talks are still in progress.

Both Washington and Seoul deny any U.S. nuclear weapons are in the South, and South Korea earlier raised the possibility of opening South Korean and U.S. bases for some form of verification by the North.

The United States "stood behind" its offer at the last arms talks to give the North a security guarantee and economic and energy aid in return for a nuclear-free peninsula, the U.S. official said. The American offer requires that the North help dismantle its nuclear program and allow monitoring before any aid is given.