LAUSANNE, Switzerland — The negotiations over Iran's nuclear program have reached a "gut check" moment, and there is a possibility that no agreement will come if certain key issues remain unresolved, U.S officials close to the talks told NBC News on Saturday.
U.S. negotiators say the toughest obstacle is getting Iran to curtail its research and development on nuclear activity while the agreement lasts — for a minimum of 10 years, but potentially longer — and in the years immediately afterward.
And Iran has not yet answered issues raised over the past 10 years by U.N. weapons inspectors about its missile warhead development.
American and allied negotiators, including France and Germany, have agreed to let Iran perfect centrifuges for medical research at its Fordow facility, but not enrich uranium that could be used for a bomb.
They have also agreed to let Iran keep 6,500 of its 20,000 centrifuges but have put other restraints on fuel and other equipment that they claim would prevent Iran from breaking out.
"The fact that President Rouhani reached out to the heads of state of the P5 + 1 is hopefully a sign that Iran is ready to make some of the tough decisions it will have to as part of a comprehensive agreement," a U.S. official said.
While U.S. officials say the last two days have been trying, Iran's Foreign Minister Mohammad Javad Zarif told reporters after a meeting with his French counterpart that it was an "excellent meeting,” adding, "Both Germany and France are very serious about an agreement."
Zarif also tweeted: "In negotiations, both sides must show flexibility. We have, and are ready to make a good deal for all. We await our counterparts' readiness.”
Congress is poised when it comes back on April 14 to pass legislation imposing additional sanctions on Iran if a deal is not reached — creating more pressure on the U.S. negotiators not to extend the talks again.
After a series of frantic talks Saturday, Secretary of State John Kerry will hold his second meeting of the day with the French and the Germans. He also met separately with Zarif.
There is no final agreement on the timing of sanctions relief if a deal is reached — but there is room for flexibility. There are multiple layers of sanctions, including two types of U.N. sanctions, U.S. sanctions and European sanctions.
The deadline for a deal was to be March 31 at the latest. Kerry was to have gone to Boston on Monday to speak, along with President Obama, at the opening of the Edward M. Kennedy Institute but the current stalemate in Switzerland forced him Saturday to cancel that plan. The final technical accord — if they meet the March deadline — will not be hammered out until June.