Iranian Foreign Minister Mohammad Javad Zarif speaks to the media at the International Conference Centre of Geneva, Sunday, Nov. 24, 2013, in Geneva, Switzerland. The agreement commits Iran to curb its nuclear activities in exchange for limited and gradual sanctions relief. (AP Photo/Carolyn Kaster, Pool) Iran's ability to enrich uranium - at what levels and what speed - is a cornerstone of the deal reached Sunday between Tehran and world powers. A: This is what Iran has frequently called its "red line." Iran denies this and has agreed to even closer U.N. inspections of its nuclear facilities. The negotiations at the time faltered and Iran moved ahead with its enrichment plans. The new accord allows for the possibility of daily U.N. inspection visits.