The Central Intelligence Agency believes that North Korea should be considered a country with viable nuclear weapons even though it has not tested any, the agency told Congress in a statement recently made public.
Previous CIA assessments have said that North Korea developed nuclear devices in the early 1990s, but the evaluations left considerable doubt as to whether they were viable because the weapons had not been tested.
"There is no information to suggest that North Korea has conducted a successful nuclear test to date," the CIA said in the statement to Congress on Aug. 18. But "we assess that North Korea has produced one or two simple fission-type nuclear weapons and has validated the designs without conducting yield-producing nuclear tests."
The statement was posted recently on the Web site of the Federation of American Scientists. It did not make clear how North Korea might have validated its designs without detonating a device.
Since the mid-1980s, U.S. spy satellites have detected high-explosive testing in North Korea with the types of compression patterns indicating research to build a nuclear bomb. But there has been no evidence of a nuclear test, which would have been quickly detected by intelligence agencies.
Daniel Pinkston, an analyst with the Center for Nonproliferation Studies in Monterey, Calif., said it was possible that North Korea had confidence in its design because of technology-sharing with another nuclear-capable country, such as Pakistan.
"We can't rule out that they have the same design that has been tested elsewhere," Pinkston said.
Normally, countries are not deemed nuclear powers until they have tested nuclear devices, as India and Pakistan did in 1998.
"The standard to recognize whether a country is nuclear or not is whether they have had a successful weapons test," said Cheong Seon Whun, an analyst with the Korea Institute for National Unification in Seoul. "North Korea would only be considered a potential nuclear power like Israel."
Israel will not confirm or deny that it possesses nuclear arms, but intelligence analysts and independent experts have long believed it has 100 to 200 sophisticated nuclear weapons.
However, Cheong noted that unlike other nations suspected of having nuclear weapons, North Korea has publicly boasted of having nuclear capabilities.
"Unless we prove that the North Koreans are lying," he said, "we have to operate under the assumption that they have nuclear weapons."
North Korea expelled United Nations weapons inspectors and cranked up its nuclear facilities last year after the collapse of a 1994 treaty under which the country was to receive energy assistance in exchange for a freeze on its nuclear activity.
The U.S. has been trying to get the North Koreans to pledge anew to give up their nuclear program, but Pyongyang has demanded guarantees that the United States won't try to topple the regime of Kim Jong Il.
The question of whether the Pyongyang regime actually has the bomb has long confounded intelligence agencies. As far back as 1994, the CIA concluded that North Korea had extracted enough weapons-grade plutonium from its Yongbyon nuclear reactor to produce one or two nuclear bombs. But that assessment has been steadily upgraded in recent years.
Secretary of State Colin L. Powell said last December that the U.S. believed that the North Koreans "have a couple of nuclear weapons and have had them for years."
Analysts note that there is a long way to go between producing fissile material and perfecting the design for a bomb -- and an even greater technological leap before the bomb can be made small and light enough to mount on a missile.