LAUSANNE, Switzerland — The United States is considering letting Tehran run hundreds of centrifuges at a once-secret, fortified underground bunker in exchange for limits on centrifuge work and research and development at other sites, officials told The Associated Press.

The tradeoff would allow Iran to run several hundred of the devices at its Fordo facility, although the Iranians would not be allowed to do work that could lead to an atomic bomb and the site would be subject to international inspections, according to Western officials familiar with details of negotiations now underway. In return, Iran would be required to scale back the number of centrifuges it runs at its Natanz facility and accept other restrictions on nuclear-related work.

Instead of uranium, which can be enriched to be the fissile core of a nuclear weapon, any centrifuges permitted at Fordo would be fed elements such as zinc, xenon or germanium for separating out isotopes used in medicine, industry or science, the officials said. The number of centrifuges would not be enough to produce the amount of uranium needed to produce a weapon within a year – the minimum time-frame that Washington and its negotiating partners demand.

The officials spoke as the latest round of talks began between U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammed Javad Zarif, who are racing to meet an end-of-March deadline to reach an outline of an agreement.