Iran's nuclear program has been hampered by machine design flaws, equipment breakdowns and problems getting parts because of international sanctions, a US think-tank report said.
Tehran's atomic progress also has been slowed by the attack of the Stuxnet computer virus, according to the report by the Washington-based Institute for Science and International Security (ISIS), which was released late Monday.
Many of the problems Iran faces are with its centrifuges, the machines that churn out purified uranium which Western countries say Tehran wants for the creation of an atomic weapon.
Tehran insists that its nuclear enrichment program is peaceful, and has refused to halt enrichment or allow inspections to quell doubts and suspicions within the international community.
Iran is under four sets of UN sanctions for refusing to curtail its uranium enrichment.
"Sanctions have taken a toll and driven Iran to do things that are not normally done," such as using lower-quality local material for key centrifuge parts, said ISIS president David Albright, a former IAEA inspector.
Five to 10 years ago "it was a lot easier for Iran" to get parts abroad for its nuclear program, Albright told AFP.
The current UN sanctions set a clear and universal standard, and have effectively choked the foreign supply of parts, Albright said.
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"It's a cat and mouse game. They will try to overcome their problems," he said.
Iran currently has some 8,000 centrifuges installed at its Natanz plant, according to UN data, of which 6,000 are enriching uranium, Albright said. But those are based on a Pakistani design prone to breaking beyond repair.
Performance data from Natanz "suggests that Iran has not succeeded in overcoming these design problems," the ISIS report said.
Iran appeared ready to install as many as a thousand advanced model centrifuges by 2012, but these models include key components built without extremely strong material known as maraging steel.
Iran cannot make enough high-quality maraging steel tubes for their nuclear program, and instead is using high-strength aluminum parts and centrifuge bellows made from carbon fiber, Albright said.
The aluminum and carbon fiber parts "may pose technical challenges that increase the risk of centrifuge failure," the report said.
Yet even with a few thousand advanced centrifuges, "Iran could break out and produce enough weapon-grade uranium for a nuclear weapon using a stock of low enriched uranium relatively rapidly," ISIS said.
Ultimately, the think-tank concluded, "sanctions and other measures may only slow the pace at which Iran can procure what it needs to support its uranium enrichment program."
A diplomat with the Vienna-based International Atomic Energy Agency (IAEA) told AFP on Friday that it will issue a new report in mid-November on Iran's nuclear weapon efforts.
US-Iran tension has risen after Washington accused Tehran of being behind an alleged plot to assassinate the Saudi Arabian ambassador on US soil. Iran has denied any involvement.