GENEVA -- After almost four months of difficult negotiations, the United States and North Korea signed an agreement yesterday to end their dispute over North Korea's nuclear program but kept secret many details of how the accord will be put into effect.
The chief U.S. negotiator, Robert L. Gallucci, said the two sides had signed a separate confidential document that is more specific than the four-page "agreed framework" that was made public after its signing at the North Korean mission to the United Nations in Geneva.
He insisted that the secret document was consistent with the main agreement and would be made available on a confidential basis to senior members of Congress. "Documents of this sort are not unusual in international agreements," he added.
Mr. Gallucci implied but would not say that North Korea had requested that parts of the agreement not be divulged. "We agreed to respect the confidentiality of this document," he said.
The document is believed to address some of the questions raised by the public agreement, notably the issue of when North Korea will ship abroad some 8,000 fuel rods that are now being kept in a cooling pond and could in theory be processed into weapons-grade plutonium.
Under the broad agreement concluded in Geneva on Monday, North Korea will freeze its nuclear activities, renounce any ambition to become a nuclear power and eventually open two secret military sites to inspection by international experts so they can determine whether Pyongyang already has nuclear capability.
In exchange, an international consortium will replace North Korea's current graphite nuclear reactors with new light-water reactors, which are considered less dangerous because they produce little weapons-grade plutonium. The United States also agreed to low-level diplomatic ties with North Korea.
After the accord was signed yesterday, North Korea's chief negotiator, Kang Sok Ju, described it as "a very important milestone document" that would resolve his country's nuclear dispute with the United States "once and for all."
He said the agreement, once put into effect, would resolve "all questions of the so-called nuclear weapons development by North Korea" that have raised "such unfounded concerns and suspicions."
"We have neither the intention nor the plan to develop nuclear weapons," Mr. Kang said.