ISTANBUL (AP) - The U.S. is joining five other world powers for talks with Iran this week publicly confident that international efforts have slowed Tehran's capacity to make nuclear arms and created more time to press Tehran to accept curbs on its atomic activities.
But the Federation of American Scientists is warning against complacency. It says there have been impressive improvements in the performance of the Iranian machines that enrich uranium - an activity that has provoked U.N. sanctions because it could be used to make nuclear weapons.
In a study shared with The Associated Press ahead of publication, the Washington-based organization argues that Iran last year appears to have increased efficiency of the machines that produce enriched uranium by 60 percent, giving it the technical capacity to produce enough material for a simple nuclear warhead in 5 months.
Still, Washington has joined diplomats and officials at the International Atomic Energy Agency - the U.N. monitor of Iran's nuclear program - in saying the nation is struggling with uranium enrichment, a process that can create both nuclear fuel and fissile warhead material.
And Israel, Iran's implacable foe and considered to have the Mideast's best intelligence on Iran's nuclear strivings, has agreed.
So Washington's message is essentially this: There is more time to negotiate with Iran in the hope that it will come around and give up enrichment - thereby removing the threat of an Israeli or U.S. military strike on Iran's nuclear facilities.
Iran insists it is enriching only to make nuclear fuel, and Ivanka Barzashka, author of the Federation of American Scientists study, emphasizes that Tehran is unlikely to provoke the world - and increase the likelihood of attack - by kicking out IAEA inspectors and re-calibrating its centrifuges from making low-enriched to weapons grade uranium.
Olli Heinonen, who retired late last year as the IAEA deputy director general in charge of the agency's Iran file, called the likelihood of such a "breakout scenario" as a "suicidal mission" and noted that manufacturing nuclear warhead material is only one step in making a weapon. But he also said he cannot "dispute the correctness of the figures" in the study.
The two sides are coming to the table at Istanbul for Friday's talks as far apart as they were at the end of their first round in Geneva last month. Barzashka said that efforts to bridge the divide must be increased.
"The biggest issue with recent statements that Iran's nuclear drive has been slowed down is that we are getting a false sense of security that we have bought more time," Barzashka said in an e-mail. "That takes away from the urgency ... (of) a diplomatic breakthrough."