David Albright and Corey Hinderstein, both analysts, wrote in a report issued on Friday by a Washington-based think-tank: "Given another year to make enough HEU (highly enriched uranium) for a nuclear weapon and a few more months to convert the uranium into weapon components, Iran could have its first nuclear weapons in 2009."
The findings, based on the results of UN inspections showing the pace of Iran's nuclear activities, were tentative and it remained unclear how long it would take Tehran to master uranium enrichment, the report from the Institute for Science and International Security (ISIS) said.
The report said: "This result reflects a worst case assessment, and thus is highly uncertain."
Forecasts for when Iran might secure a nuclear arsenal have differed widely. A recent US intelligence review reported by the Washington Post revised earlier assessments, saying Tehran would probably not have the bomb until 2015.
Amid mounting concern about the nature of Iran's nuclear programme, the EU and the US have condemned Iran's decision to resume uranium enrichment research and are pushing for the issue to be referred to the Security Council.
Both the EU and the US want to
refer Iran to the Security Council
Iran insists its programme is purely peaceful and has threatened to cut off co-operation with international inspectors if the matter is taken up by the UN Security Council.
The timetable of a possible weapons programme depends on how quickly Iran could build large numbers of centrifuges and then refine the operation of the centrifuges for the enrichment of weapons-grade uranium, according to the report.
Iran currently has a small cascade of centrifuges, some of which broke or crashed in previous tests. But the report said once Iran mastered the operation of the small cascade, it could expand quickly towards large-scale operations for a possible weapons project.
The report said: "Once Iran overcomes the last technical hurdle of operating its test cascade, it can duplicate it and create larger cascades.
"Iran would then be ready to build a centrifuge plant able to produce significant amounts of enriched uranium either for peaceful purposes or for nuclear weapons."
When completed, a planned nuclear fuel enrichment facility could be used to produce enough highly enriched uranium to produce 25 to 30 nuclear weapons a year, it said.
David Albright, one of the report's authors, served as a UN inspector of Iraq's weapons programmes in the 1990s.