The International Atomic Energy Agency report issued Monday noted Iran's contention that it began work on the nuclear facility in 2007 in response to Bush administration threats of war as part of a plan to safeguard sensitive "organizations and activities" that could be targeted in an armed conflict.
But according to the agency report, satellite photos showed construction on the Fordow facility began in 2002, well before Iran's nuclear program became an international issue. U.S. officials previously said they first detected the site in 2006.
The U.S. and other major powers worry that Iran's nuclear research program will produce arms, an allegation Iran denies.
The discrepancy in dates is a significant measure of Iran's sincerity. Iranian officials have long argued that since their parliament refused to ratify the Additional Protocol to the Nuclear Non-Proliferation Treaty, it only has to disclose new sites to international inspectors six months before introducing them with nuclear material, a point strenuously disputed by outgoing agency chief Mohamed ElBaradei and the West.
But from December 2003 to February 2006, Iran was adhering to the Additional Protocol, obliging it to declare new sites immediately.
The incongruous chronology and the inspection of the site, already fitted with wiring, pipes and other infrastructure, also prompted the agency to question Iran about the presence of other hidden facilities.
"Iran's declaration of the new facility ... gives rise to questions about whether there were any other nuclear facilities in Iran which had not been declared to the agency," the report said. "Iran's explanation about the purpose of the facility and the chronology of its design and construction requires further clarification."
Iran's envoy to the IAEA Ali Asghar Soltanieh dismissed the report as "routine" and "repetitive," according to the Fars news agency.
A U.S. State Department spokesman, Ian Kelly, said the IAEA report "underscores that Iran still refuses to comply fully with its international nuclear obligations."
Iran has yet to definitively respond to a proposal to swap its enriched uranium for fuel rods to operate a medical research reactor, and world powers have begun buzzing about imposing new economic sanctions on the Islamic Republic.
Russia's energy minister also announced Monday that its completion of a long-delayed nuclear power plant in the Iranian port city of Bushehr would be pushed back until after this year, according to the Interfax news agency.
Iranian officials say such delays only further their misgivings about importing nuclear technology. Increasing pressure on Iran will backfire, Iranian President Mahmoud Ahmadinejad warned Monday.