IRAN: Iranian engineers have completed sophisticated drawings of a deep subterranean shaft, according to officials who have examined classified documents in the hands of US intelligence for more than 20 months.
Complete with remote-controlled sensors to measure pressure and heat, the plans for the 400m tunnel appear designed for an underground atomic test detonation that might one day announce Tehran's arrival as a nuclear power, the officials say.
By the estimates of US and allied intelligence analysts, that day remains as much as a decade away - assuming that Iran applies the full measure of its scientific and industrial resources to the project and encounters no major technical hurdles.
However, whether Iran's leaders have reached that decision and what concrete progress the effort has made remain divisive questions among government analysts and UN inspectors.
In the three years since Iran was forced to acknowledge having a secret uranium enrichment programme, western governments and UN nuclear watchdog the International Atomic Energy Agency have amassed substantial evidence to test the Tehran government's assertion that it plans to build nothing more than peaceful nuclear power plants.
Often circumstantial, usually ambiguous and always incomplete, the evidence has confounded efforts by policymakers, intelligence officials and allies to reach a confident judgment about Iran's intentions and a diplomatic solution to the crisis. Drawings of the unbuilt test site, not disclosed publicly before, appear to US officials to signal at least the ambition to test a nuclear explosive.
US and UN experts who have studied them say the undated drawings do not clearly fit into a larger picture. Nowhere, for example, does the word "nuclear" appear. The authorship is unknown and there is no evidence of an associated programme to acquire, assemble and construct the components of such a site.
"The diagram is consistent with a nuclear test-site schematic," a senior source said, noting that the drawings envision a test control team parked a safe 10km away from the shaft. As far as US intelligence knows, the idea has not left the drawing board.
Other suggestive evidence is cloaked in similar uncertainty. Contained in a laptop stolen by an Iranian citizen in 2004 are designs by a firm called Kimeya Madon for a small-scale facility to produce uranium gas, the construction of which would give Iran a secret stock that could be enriched for fuel or for bombs.
Also on the laptop - obtained by US intelligence - were drawings on modifying Iran's ballistic missiles in ways that might accommodate a nuclear warhead.
Beyond the computer files, an imprisoned Pakistani arms dealer recently offered uncorroborated statements that Iran received several advanced centrifuges, equipment that would vastly improve its nuclear knowledge.
US intelligence considers the laptop documents authentic but cannot prove it. Analysts cannot completely rule out the possibility that internal opponents of the Iranian leadership could have forged them to implicate the government, or that the documents were planted by Tehran to convince the West that its program remains at an immature stage.
CIA analysts, some of whom had been involved only a year earlier on the flawed assessments of Iraq's weapons programmes, initially speculated that a third country, such as Israel, might have fabricated the evidence, but they eventually discounted that theory.
British intelligence, which was asked for a second opinion, concurred last year that the documents appeared authentic.
German and French officials consider the information troubling, sources said, but Russian experts have dismissed it as inconclusive. IAEA inspectors, highly sceptical of US intelligence on Iraq, have begun to pursue aspects of the laptop information that appear to bolster previous leads.
Bush administration officials, convinced that Iran has a weapons programme, believe the body of documentation is the nearest anyone can expect to "smoking gun" evidence.
Even in the US government, the predominant interpretation is more complex.
Any step toward uranium enrichment, experts say, is consistent with three competing explanations - that Iran's programme is peaceful, that it aims for a weapon, or that the Tehran government is still keeping its options open.
Director general of the IAEA Mohamed ElBaradei said that after three years of investigation, he still could judge Iran's program "exclusively peaceful".
At the same time, Iran is "not an imminent threat," he said in a recent interview.