La questione viene affrontata in un articolo dello storico Bullettin of the Atomic Scientists:
When could Iran get the Bomb?
What we know and what we don’t know about Iran’s nuclear program.
Despite this caution, a handful of U.S. officials have since attempted to overstate Iran’s nuclear progress, contradicting even this latest estimate. It appears that in the ongoing crisis between Iran and the United States, the crucial struggle for public perception of the Iranian nuclear threat is well under way.
Following an International Atomic Energy Agency (IAEA) briefing of U.N. Security Council permanent members and Germany in mid-March about a group of 164 centrifuges at Iran’s Natanz uranium enrichment site, U.S. officials began to distort what the IAEA had said. Under the cloak of anonymity, these officials told journalists that Iran’s actions represented a significant acceleration of its enrichment program. The IAEA was "shocked," "astonished," and "blown away" by Iran’s progress on gas centrifuges, according to these U.S. officials, leading the United States to revise its own timeline for when Iran will get the bomb. In reality, IAEA officials said they were not surprised by Iran’s actions. These U.S. statements, a senior IAEA official told the Associated Press, came "from people who are seeking a crisis, not a solution." 
Some outside experts and officials, including Defense Secretary Donald Rumsfeld, may be trying to undermine U.S. intelligence assessments on Iran’s timeline to the bomb by highlighting the intelligence community’s failure to correctly assess Iraq’s weapons of mass destruction efforts.  Although the intelligence community deserves strong criticism for its analysis of Iraq’s weapons programs, the more recent Iranian analysis has been subject to more thorough review and is more consensual than the Iraqi assessments. For example, centrifuge experts at Oak Ridge National Laboratory, who challenged faulty CIA conclusions that Iraqi aluminum tubes were for a reconstituted nuclear weapons program long before the war, have been central in assessing Iran’s gas centrifuge program for the intelligence community, according to a U.S. intelligence official.
Iran is indeed on the verge of mastering a critical step in building and operating a gas centrifuge plant that would be able to produce enriched uranium for either peaceful or military purposes. However, it can be expected to face serious technical hurdles before it can reliably produce large quantities of enriched uranium.
Many details about Iran’s technical nuclear capabilities and plans are unknown, and the IAEA has neither been able to verify that Iran has declared its nuclear activities in full nor to establish conclusively that Iran does not have hidden nuclear enrichment sites. Western governments view with skepticism Iranian denials of intentions to produce highly enriched uranium (HEU) or to build nuclear weapons. Yet there is no evidence of an Iranian decision to build a nuclear arsenal, let alone any knowledge of an official Iranian schedule for acquiring nuclear weapons.
During the past three years of IAEA inspections, the international community has learned a great deal of information about the Iranian program that can be used to estimate the minimum amount of time Iran would need to produce enough HEU for a nuclear bomb. According to several possible scenarios, Iran appears to need at least three years before it could have enough HEU to make a nuclear weapon. Given the technical difficulty of the task, it could take Iran much longer.
With political rhetoric likely to intensify during the coming months, it is essential to have as clear an evaluation as possible of Iranian nuclear capabilities. It is also essential to avoid repeating the mistakes that were made prior to the Iraq War, when senior Bush administration officials and their allies outside government hyped the Iraqi nuclear threat to gain support in confronting Iraq.