Iran has been significantly increasing its output of low-enriched uranium and if it was further refined could make at least five nuclear weapons, according to a US thinktank.
The Institute for Science and International Security, which tracks Iran's nuclear programme, made the analysis on the basis of data in the latest quarterly report of the International Atomic Energy Agency (IAEA).
The UN watchdog's report, which was published on Friday, showed that Iran is pressing ahead with its uranium enrichment work in defiance of UN resolutions calling on it to suspend the activity.
It is said that Iran had produced almost 6.2 tonnes of uranium enriched to a level of 3.5% since it began the work in 2007 some of which has subsequently been further processed into higher-grade material.
This equates to nearly 750 kg more than in the previous IAEA report issued in February, and the thinktank said Iran's monthly production had risen by tremendously by a third.
"This total amount of 3.5% low enriched uranium hexafluoride, if further enriched to weapon grade, is enough to make over five nuclear weapons," its analysis said.
But the thinktank added that some of Iran's higher-grade uranium had been converted into reactor fuel and would not be available for nuclear weapons, at least not too quickly.
Enriched uranium can be used to fuel power plants, which is Iran's stated purpose, or to provide material for bombs, if refined to a much higher degree. The west suspects that may be Iran's ultimate goal despite the Islamic Republic's denials.
Iran began enriching uranium to a fissile concentration of 20% in 2010, saying it needed this to fuel a medical research reactor. It later expanded the work sharply by launching enrichment at an underground site, Fordow.
It alarmed a suspicious west since such enhanced enrichment accomplishes much of the technical leap towards 90% or weapons-grade uranium.
The IAEA report said Iran had added another 350 enrichment centrifuges to the existing 700 at Fordow, which is buried deep under rock and soil to protect it against any enemy attacks.
Although not yet being fed with uranium, the new machines could be used to further boost Iran's output of uranium enriched to 20%.
The Institute for Science and International Security said Iran still appeared to be experiencing problems in its testing of production-scale units of more advanced centrifuges that would allow it to refine uranium faster, even though it had made some progress.