Iran nuclear talks ended last week with enthusiastic pronouncements of progress from negotiators. But diplomats say significant gaps remain between what the Iranians offered and what world powers seek in order to reduce fears the country wants to build nuclear weapons.
A key concern is the size and output of Iran's enrichment program.
Iran denies any interest in nuclear arms. It is running over 10,000 centrifuges that have created tons of reactor fuel-grade material that can be further enriched to arm nuclear warheads. That's a relatively slow process with such material.
Tehran also has nearly 440 pounds (200 kilograms) of higher-enriched uranium in a form that can be turned into weapons much more quickly.
Two diplomats well-informed about the talks demanded anonymity because they are not authorized to discuss them.