As the US Congress debate further sanctions, the report found thatIran's banking system was under growing stress and would have little capacity to defend its currency if it came under renewed pressure.
The state of Iran's finances helped explain the sudden insistence of Iran's new president Hassan Rouhani on a "quick", three-to-six month deal being brokered between Tehran and the international P5+1 grouping. Talks are due to open in Geneva on October 15.
"We think the reaction of Rouhani this past week and his desire for a short-term deal can be partly explained by the fact that Iran's finances are much worse than he and his team had expected to see when they first entered office," said Mark Dubowitz of the Foundation for Defence of Democracies a think-tank that has urged a tough line on Tehran.
"We believe that Iran is less than a year from reaching critical nuclear capability, despite these international sanctions that have been designed to prevent Iran from doing so," said Mr Dubowitz, citing reserves held Iran's Supreme Leader and the Revolutionary Guard.
"But our assessment is that Iran's political timeline may be considerably shorter because there is considerable pressure on Rouhani to deliver on his commitment to get sanctions lifted, oil flowing and the economy stabilized as quickly as possible."