LAUSANNE, Switzerland — Negotiations over Iran’s nuclear program grew frantic on Saturday amid signs of discord, with the French and German foreign ministers joining U.S. Secretary of State John Kerry in talks with Tehran’s top diplomat ahead of an end-of-March deadline for a preliminary deal.

With just four days to go until that target, negotiators here were meeting multiple times in various formats to produce what they hope will be an outline of an agreement that can become the basis for a comprehensive deal to be reached by the end of June. The U.S. State Department said “serious but difficult work” remained for negotiators, with the pace of discussions expected to intensify as “we assess if an understanding is possible.”

In another nod to the fast-approaching deadline, Iranian President Hassan Rouhani spoke by phone with German Chancellor Angela Merkel to emphasize the importance of reaching an agreement.

Iranian negotiator Majid Takht-e Ravanchi denied a report that the sides were close to agreement on a text, and other officials spoke of remaining obstacles, including Iranian resistance to limits on research and development and demands for more speedy and broad relief from international sanctions.

Iran says its nuclear ambitions are peaceful; other nations fear it is seeking to develop weapons.

Progress has been made on the main issue: The future of Iran’s uranium enrichment program. It can produce material for energy, science and medicine, but also for the fissile core of a nuclear weapon.

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The sides tentatively have agreed that Iran would run no more than 6,000 centrifuges at its main enrichment site for at least 10 years, with slowly easing restrictions over the next five years on that program and others Tehran could use to make a bomb.

The fate of a fortified bunker previously used for uranium enrichment also appears closer to resolution. Officials have told The Associated Press that the U.S. may allow Iran to run hundreds of centrifuges at the Fordo bunker in exchange for limits on centrifuge work and research and development at other sites. The site would be subject to international inspections.

Also problematic is Iran’s research and development program. Tehran would like fewer constraints on developing advanced centrifuges than the U.S. is willing to grant.

Also in dispute is the fate of economic penalties against Iran.

In addition, questions persist about how Iran’s compliance with an agreement would be monitored.


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