Mark Dubowitz, director of the Foundation for Defense of Democracies and an advocate of tougher sanctions who has testified before Congress, said the amount of accessible reserves is "the single most important piece of intelligence that U.S. policymakers today need to know." He said that will determine whether "the Iranians drop dead economically before or after they reach undetectable nuclear breakout."
A widely cited report last month by the Washington-based Institute for Science and International Security concluded that Iran will be able to produce enough weapons-grade uranium by mid-2014 for a nuclear breakout, or a quick dash to a bomb, possibly within weeks. The breakout could be so fast that international watchdogs and Western intelligence might not be able to detect it.
Proponents of sanctions hope that the drag on the economy will force Iran to switch course. But trying to discern the true dimensions of the economic impact is almost impossible because authorities either release data with long lag times or do not report numbers accurately.
Outside sources of information are sparse.
The International Monetary Fund estimated foreign reserves were down to $80 billion in March from $96 billion a year earlier. The $80 billion is still a healthy level, but it's not clear how much of the money is accessible and how much is frozen in accounts overseas by sanctions.
Economic Research firm Roubini Global Economics and Dubowitz's Foundation for Defense of Democracies assessed in a new draft report that $30 billion to $50 billion of reserves is accessible. But the figures cannot be independently verified.
Still, analysts say Iran's economy has proved so far to be resilient and flexible enough to offset some sanctions damage. And the rial's devaluation has one advantage — it has made exports cheaper and thus more appealing. That has helped the country diversify its exports and become less reliant on sanctioned oil.
Iran boosted exports of non-oil goods that are not subject to sanctions by 20 percent in 2012, according to the Institute of International Finance (IIF), an economic think tank. Those include oil byproducts such as petrochemicals as well as cement, iron ore, pistachios and Persian carpets.
Oil remains Iran's dominant export and Garbis Iradian, deputy director of the IIF's Africa and Middle East Department, said Iran can withstand sanctions for a long while if prices do not drop sharply.
"As long as oil prices stay at around $100, the sanctions have a negative impact, but it's OK, they can survive for several years. If oil prices drop below $80, they will feel the impact of sanctions," he said.
Meanwhile, U.S. lawmakers are looking to further tighten sanctions. The House of Representatives approved a bill last month that, if it becomes law, would further limit Iran's access to its foreign currency reserves and impose a virtual oil and trade embargo. It would commit the U.S. to the goal of ending all Iranian oil sales worldwide by 2015 — the year after some experts estimate Tehran could build a bomb.
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