Six world powers and Iran announced the outline of a preliminary deal Thursday that Western officials say will impose sweeping restrictions on Iran's nuclear activities for more than a decade.
Concluding a marathon bout of negotiations, diplomats laid out an unexpectedly detailed plan that Western officials said would cut Iran's capability to enrich uranium by two-thirds for the next 10 years and impose other limits lasting up to 25 years.
The plan, which did not produce a signed document, would give Iran substantial relief from U.S., European and United Nations sanctions. But the gradual phase-out of sanctions would depend on Iran's compliance with its obligations under the deal and probably would not start before next year.
The proposed deal calls for Iran to cut its enriched uranium stockpile by 98% and to halt sensitive nuclear research and development for a decade, according to the Western officials. It also would limit Iran to enriched uranium far below weapons grade for at least 15 years, and require Tehran to destroy or remove the core of the country's only reactor capable of producing plutonium, another potential fuel for nuclear arms.
If successful, the accord could neutralize the most worrisome security threat facing the West and its allies in the Middle East, which has spiraled into sectarian conflicts and revolts, many fueled by Iran. But Iranian officials did not publicly confirm many of the key nuclear concessions that other governments involved in the negotiations announced, raising doubts about whether Tehran's leaders have fully signed on.
The deal starts the clock on the next round of diplomacy. Iran and a six-nation diplomatic bloc — the United States, Britain, France, China, Russia and Germany — have three months to resolve remaining disputes and fill in the technical details to complete a binding, comprehensive agreement.
Resolving the nuclear standoff with Iran has been a top foreign policy priority for President Obama; Iran, which denies it is seeking a nuclear weapon, is desperate to escape sanctions that have crippled its economy. Both governments claimed partial success Thursday.
"Solutions on key parameters of Iran #nuclear case reached. Drafting to start immediately, to finish by June 30," Iran's president, Hassan Rouhani, wrote on Twitter before the deal was announced.
Appearing an hour or so later in the Rose Garden, Obama hailed what he called a "historic understanding with Iran, which, if fully implemented, will prevent it from obtaining a nuclear weapon."
Obama sought to reassure skeptics in Congress and the public that the accord "would cut off every pathway that Iran could take to develop a nuclear weapon" and said Iran would undergo "the most robust and intrusive inspections and transparency regime" imposed on a nuclear program.
"This deal is not based on trust," he said. "It's based on unprecedented verification."
He said he had spoken by phone with the leaders of Britain, France, Germany and Saudi Arabia, as well as congressional leaders. He later called Israeli Prime Minister Benjamin Netanyahu, who has sharply criticized the negotiations.
According to a White House statement, Obama said he has "directed his national security team to increase consultations with the new Israeli government about how we can further strengthen our long-term security cooperation with Israel and remain vigilant in countering Iran's threats."
But in a statement issued after the call, Netanyahu said, "A deal based on this framework would threaten the survival of Israel.
"This deal would legitimize Iran's nuclear program, bolster Iran's economy, and increase Iran's aggression and terror throughout the Middle East and beyond."
Iran's state-run media called the agreement a success, and drivers honked horns and waved flags in Tehran's busy streets to celebrate a deal that could ease sanctions that have affected daily life for millions. Many Iranians have been glued to the TV and the Internet for days, watching the ups and downs of the roller-coaster talks.
The next round of negotiations could be even more contentious than the recent talks, however, and could still fail. Critics in Washington, Tehran and elsewhere are sure to find fault with the proposed pact and to demand new concessions from the other side.
Ilan Goldenberg, a former Obama administration Mideast specialist, said the next three months will be "painstakingly difficult" and are again likely to bring the process to the brink of collapse.
Negotiators missed three self-imposed deadlines in the last 18 months, including one this week. Talks repeatedly appeared close to collapse in the latest round, which lasted eight grueling days.
Secretary of State John F. Kerry and Iranian Foreign Minister Mohammad Javad Zarif appeared satisfied but exhausted after the final round of talks, which included an all-nighter that lasted until 6 a.m. Thursday and at least one near-meltdown. U.S. officials said the deal finally fell into place about 10 a.m.
"We have taken a decisive step," European Union foreign policy chief Federica Mogherini and Zarif said in a joint statement they each read to reporters. "We have reached solutions on all key parameters."
But Zarif and other Iranian officials did not acknowledge some of the details that Washington and other governments announced. That may give Iran leeway to dispute what the major powers laid out in their description of the deal, analysts said.
Most U.S. and European Union sanctions won't be suspended until Iran has curtailed its nuclear program enough to extend to a full year the time it would take to accumulate enough nuclear fuel for one nuclear weapon, officials said. Once a deal is signed, Iran probably will need six months to a year to meet the requirements, officials said, and sanctions would snap back in place if Iran is judged to have violated its commitments.
U.S. sanctions on Iran for terrorism, human rights abuses and ballistic missiles will remain in place under the deal.
All United Nations sanctions also will be lifted once international inspectors confirm that Iran has met its obligations under the deal, including the required downgrading of operations at Natanz, Arak and Fordow. A new U.N. Security Council resolution would maintain restrictions on transfers of sensitive technologies and other limits.
The two sides still must negotiate how soon that would occur. Iran had sought to get the U.N. sanctions lifted immediately.
The deal doesn't require Iran to close any of its nuclear facilities, and Zarif told reporters that was a key condition for his negotiating team.
But the bomb-resistant Fordow enrichment facility, built inside a mountain, will be converted to other research activities. It will not be used to enrich uranium, or even allowed to store fissile material, for 15 years.
The Natanz facility will reduce the number of operating centrifuges, the fast-spinning devices that purify uranium for weapons, to 5,060, about a third of the current total. Iran also agreed to not enrich uranium over 3.67%, far below weapons grade, for at least 15 years and to use only rudimentary, first-generation centrifuges.
The core of the reactor at the Arak heavy-water facility, which officials feared could have been used to produce weapons-grade plutonium, will be destroyed or removed from the country. Iran instead will install a reactor for peaceful nuclear research and radioisotope production.
Republicans in Congress were quick to raise doubts. Rep. Ed Royce (R-Fullerton), chairman of the House Foreign Affairs Committee, said the deal left unanswered many questions, such as what kind of research and development Iran will be permitted, the extent of the sanctions relief it will receive and how the international community would respond if Iran violates the agreement.
"The administration owes Congress the details on many key questions from today's announcement," he said in a statement.