Centrifuges. Sanctions. Nuclear research. Sticking points remain on some of the most basic issues as negotiations between world powers and Iran over Tehran's nuclear program hit crunch time.
Tuesday is the deadline for the two sides to finalize a framework agreement. That deal, if it can be reached, is supposed to be the basis for a final accord by the end of June detailing steps for Iran to scale back its uranium enrichment and other technology that could be used to make nuclear arms.
In return, Tehran would be rewarded with the easing of crippling economic sanctions.
U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif have done most of the top-level negotiating in recent months. But the talks formally remain between Iran and six nations — the U.S., Russia, China, Britain, France and Germany — and the foreign ministers of six of those seven countries are now in the Swiss city of Lausanne.
As they try to bridge remaining gaps, here is a look at where the talks stand.
Officials in Lausanne say the sides are advancing on points that discuss cuts and limits to aspects of Iran's enrichment program. Over the past weeks, Iran has moved from demanding that it be allowed to keep nearly 10,000 centrifuges enriching uranium, to agreeing to 6,000. Tehran may now be ready to accept even fewer but is said to be pushing back on how long it must limit the technology it could use to make atomic arms.
It also insists that sanctions be lifted immediately as part of a deal. The Obama administration wants to suspend or remove them more slowly.
The United States says any deal will stretch the time Iran would require to make a nuclear weapon from the present two-to-three months to at least a year. But critics question that, and object that such an agreement would keep Tehran's nuclear technology intact.
WHERE ELSE IS THERE PROGRESS?
Iran and the six powers at the table have moved close on what to do with a nearly built reactor that was also a proliferation concern because it would have produced enough plutonium for several nuclear bombs a year. The facility would be re-engineered to generate only a fraction of the material.
Officials say the sides also are seriously discussing turning a formerly secret underground uranium enrichment plant into a facility that would make isotopes for medical, industrial and scientific uses.
If used for uranium enrichment the bunker would be a concern, because it is thought impervious to air attack — an option neither Israel nor the U.S. have ruled out should diplomacy fail. But — although it would not be enriching uranium — the facility would use the same technology as for uranium enrichment, and critics say that leaves potential bomb-making infrastructure intact.
WHERE ARE THE GREATEST PROBLEMS?
The sides differ sharply on how and when to lift sanctions that started to be imposed nearly a decade ago in attempts to force Iran to curb its atomic activities.
Iran wants all sanctions lifted up front as soon as a deal is struck. The U.S. and its allies are opposed because they would lose the penalties as a lever in case Tehran reneges on its commitments. They want gradual lifting over much of the length of any agreement — if not all of it.
Iran's research and development of centrifuges and related technology also remains at dispute. Iran wants few, if any limits on R&D, but the other side sees potentially major advances as a problem that would counter the idea of freezing activities that could be applied to nuclear weapons manufacture.
There also are differences on the length of any deal. Iran insists on 10 years and is resisting a push to extend that time by at least another five years of slowly easing restrictions on its program. Alluding to the dispute, German Foreign Minister Frank-Walter Steinmeier said Monday, "The issue here is more than 10 years. We have more ambitious expectations."
WHAT'S OFF THE TABLE?
The six powers originally insisted that any final deal include a ruling by the U.N.'s International Atomic Energy Agency on allegations that Tehran has worked secretly in the past on nuclear arms — something Iran denies, saying the allegation is based on intelligence doctored by its foes. With the IAEA probe deadlocked, and Iran offering no indications it will cooperate, any agency findings likely will be delayed for months, if not years, much too late for the June deadline.
Washington and its allies initially said that Iran must agree to restrictions on its missile technology, which they say could be used to deliver a nuclear warhead. Tehran has fiercely resisted inclusion of that subject, however, and diplomats say the topic has not been part of formal discussions for weeks.