LAUSANNE, Switzerland — Iran may accept new constraints to its uranium enrichment program at nuclear talks but is pushing back on how long it must accept limits on technology it could use to make nuclear arms, Western officials said on Sunday. The officials spoke less than four days ahead of Tuesday's target date for a preliminary agreement. That accord is meant to set the stage for a further round of negotiations toward a comprehensive deal aimed at imposing long-term curbs on Iran's nuclear activities in return for sanctions relief. Foreign ministers and other representatives of Iran and the six powers it is negotiating with have said that despite significant obstacles, the talks have a chance of succeeding by Tuesday. The two officials demanded anonymity in exchange for outlining the state of the talks because they are not authorized to discuss them publicly. The sides are advancing on limits to aspects of Iran's uranium enrichment program — which can be used to make the core of a nuclear warhead, they said. Iran over the past weeks moved from demanding it be allowed to keep 10,000 centrifuges enriching uranium, to agreeing to 6,000. The officials said Sunday that it now may be ready to accept even less. Tehran also is ready to ship out all of the enriched uranium it produces to Russia — a change from previous demands that it be allowed to keep a small amount in stock, the officials said. One of them, however, cautioned that Iran had previously agreed to this but changed its mind. Uranium enrichment has been the key concern in over more than a decade of international attempts to cap Iran's nuclear programs. Tehran says it wants to enrich only for energy, science, industry and medicine, but many nations fear it could use the technology to make weapons-grade uranium. The United States and its allies are seeking a deal that stretches the time Iran would need to make a nuclear weapon from the present two to three months to at least a year. The officials said differences on the length of an agreement remains one of the main disputes. Iran, they say, wants a total lifting of all caps on its activities after 10 years, whereas the US and others at the talks — Russia, China, Britain, France and Germany — insist on progressive removal after a decade of pervasive limits. One official said the two sides may give differing interpretations of any deal — the Iranians insisting that they are free to do what they want after 10 years, the others listing areas where restrictions remain. Limits on Iran's research and development of centrifuges also remain unresolved, said the officials. Tehran has created a prototype centrifuge that it says enriches uranium 16 times faster than its present mainstay model. The US and its partners want to constrain research on such and other advance models, because it would greatly increase the speed that Tehran could make enough weapons-grade uranium for a bomb, once limits on its programs are lifted. One of the officials said Russia remains opposed to American insistence that any UN sanctions lifted in the course of a deal be quickly re-imposed in case Tehran reneges on any commitments, saying Moscow fears establishing a precedent. Both said monitoring remains a problem, with Iran resisting attempts to make inspections and other ways to make sure there is no cheating as intrusive as possible. There is tentative agreement on turning a nearly-finished reactor into a model that gives off less plutonium waste than originally envisaged. Plutonium, like enriched uranium, is a pathway to nuclear weapons. Iran and the US are discussing repurposing an underground bunker Iran used to enrich uranium to let Iran run centrifuges there. Instead of enriching uranium, the machines would produce isotopes for peaceful applications, they said. With the deadline close and problems remaining, US Secretary of State John Kerry canceled plans Sunday to return to the United States for an event honoring his late Senate colleague Edward Kennedy and negotiators were meeting multiple times in various formats. Kerry has been in discussions with Iranian Foreign Minister Mohammad Javad Zarif in the Swiss town of Lausanne since Thursday. — AP
