But in private, Iranian officials have voiced a willingness to work with the United States on IS, though not necessarily on the battlefield. U.S. Secretary of State John Kerry said on Friday that Iran has a role to play in defeating Islamic State, indicating the U.S. position may also be shifting.
"Iran is a very influential country in the region and can help in the fight against the ISIL (IS) terrorists ... but it is a two-way street. You give something, you take something," said a senior Iranian official on condition of anonymity.
"ISIL is a threat to world security, not our (nuclear) program, which is a peaceful program," the official added.
Tehran rejects Western allegations that it is amassing the capability to produce atomic weapons under cover of a civilian nuclear energy program.
Another Iranian official echoed the remarks. Both officials said they would like the United States and its Western allies to show flexibility on the number of atomic centrifuges Tehran could keep under any long-term deal that would lift sanctions in exchange for curbs on Tehran's nuclear program.
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"Both sides can show flexibility that will lead to an acceptable number for everyone," another Iranian official said.
West wants to keep atomic talks separate
Western officials told Reuters that Iran has not raised this idea in nuclear negotiations with the United States, Britain, France, Germany, Russia and China that resumed in New York on Friday. Diplomats close to the talks say they are unlikely to settle in New York on a long-term accord that would lift sanctions in exchange for curbs on Iranian nuclear work.
The Western officials said it would be difficult for them to even discuss the point in the atomic negotiations as the United States and its allies are determined to keep the nuclear negotiations focused exclusively on atomic issues as the Nov. 24 deadline for a deal nears.
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Iran ready to work with US on ISIS