Two of the biggest areas of disagreement are what's going to happen to Iran's current stockpile of low-enriched uranium (LEU), and when sanctions are going to be lifted.
While U.S. officials said that Iran agreed to reduce its LEU stores from 9,000 to 300 kilograms, and that it will not convert those resources to fuel, Tehran has specifically said that it can use the existing stockpile to build something the Iranian fact sheet calls a "nuclear fuel center." That may be a reference to a nuclear fuel production facility Iran first proposed in 2006.
As for sanctions, the U.S. has insisted that it will drop nuclear-related penalties on Iran only when it has evidence that the Islamic Republic has addressed "key" parts of the deal. Iranian leaders, meanwhile, said they require all Western sanctions removed as soon as the deal is signed.
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"We will not sign any deal unless all sanctions are lifted on the same day.... We want a win-win deal for all parties involved in the nuclear talks," Iranian President Hassan Rouhani said in a televised speech on Thursday.
Iran's Supreme Leader Ayatollah Ali Khamenei reportedly took a more combative tone in a Thursday address, suggesting that the fact sheet discrepancies could be a tactic from the "devilish" American government.
"Americans put out a statement just a few hours after our negotiators finished their talks ... this statement, which they called a 'fact sheet,' was wrong on most of the issues," Khamenei said, according to Reuters.