he United States and Iran are working on a two-phase deal that clamps down on Tehran's nuclear program for at least a decade before providing it leeway over the remainder of the agreement to slowly ramp up activities that could be used to make weapons.
GENEVA — The United States and Iran are working on a two-phase deal that clamps down on Tehran's nuclear program for at least a decade before providing it leeway over the remainder of the agreement to slowly ramp up activities that could be used to make weapons.
Officials from some of the six-power talks with Iran said details still needed to be agreed on, with U.S. and Iranian negotiators meeting Monday for the third straight day ahead of an end-of-March deadline for a framework agreement. U.S. Secretary of State John Kerry joined the negotiations after arriving Sunday.
A breakthrough was not expected before Kerry returns to Washington later Monday. Still, Western officials familiar with the talks cited long-awaited progress on some elements that would have to go into a comprehensive deal. They described the discussions as a moving target, however, meaning changes in any one area would have repercussions for other parts of the negotiation.
The idea would be to reward Iran for good behavior over the last years of any agreement, gradually lifting constraints on its uranium enrichment program and slowly easing economic sanctions.
Iran says it does not want nuclear arms and needs enrichment only for energy, medical and scientific purposes, but the U.S. fears Tehran could re-engineer the program to another potential use — producing the fissile core of a nuclear weapon.
The U.S. initially sought restrictions lasting for up to 20 years; Iran had pushed for less than a decade. The prospective deal appears to be somewhere in the middle.
One variation being discussed would place at least 10-year regime of strict controls on Iran's uranium enrichment program. If Iran complies, the restrictions would be gradually lifted over the last five years of such an agreement.
Iran could be allowed to operate significantly more centrifuges than the U.S. administration first demanded, though at lower capacity than they currently run. Several officials spoke of 6,500 centrifuges as a potential point of compromise, with the U.S. trying to restrict them to Iran's mainstay IR-1 model instead of more advanced machines.
It would also be forced to ship out most of the enriched uranium it produces or change it to a form that is difficult to reconvert for weapons use. It takes about 1 ton of low-enriched uranium to process into a nuclear weapon, and officials said that Tehran could be restricted to an enriched stockpile of no more than 300 kilograms (about 700 pounds).
The officials represent different countries among the six world powers negotiating with Iran — the United States, Britain, China, France, Germany and Russia. They spoke on condition of anonymity because they were not authorized to talk publicly about the negotiations.
The U.N. nuclear agency would have responsibility for monitoring, and any deal would depend more on technical safeguards than Iranian goodwill to ensure compliance.
But the accord will have to receive some sort of acceptance from the U.S. Congress to be fully implemented. That is a tough sell given the hostility to any Iranian enrichment from most Republican and many Democratic lawmakers.
For the United States, the goal is to extend to at least a year the period that Iran would need to surreptitiously "break out" toward nuclear weapons development.
In exchange, Iran wants relief from the various layers of trade, financial and petroleum sanctions crippling its economy and the Americans are talking about phasing in such measures.
Several steps would come immediately through executive action by President Barack Obama, the officials said. Other penalties would be suspended, but not lifted, as Iran demonstrates its compliance with its obligations. A lesser amount of restrictions would stay in place until Congress acts to remove them permanently.
Progress also is being made on the status of Iran's underground enrichment facility at Fordo and heavy water reactor at Arak, which potentially could produce enough plutonium for several nuclear weapons a year. Fordo could be turned into a research lab and Arak, which is close to completion, could be reconfigured to produce much less plutonium, officials said.