LAUSANNE, Switzerland — Capping exhausting and contentious talks, Iran and world powers sealed a breakthrough agreement Thursday outlining limits on Iran's nuclear program to keep it from being able to produce atomic weapons. The Islamic Republic was promised an end to years of crippling economic sanctions, but only if negotiators transform the plan into a comprehensive pact.
They will try to do that in the next three months.
The United States and Iran, long-time adversaries who hashed out much of the agreement, each hailed the efforts of their diplomats over days of sleepless nights in Switzerland. Speaking at the White House, President Barack Obama called it a "good deal" that would address concerns about Iran's nuclear ambitions. Iranian Foreign Minister Mohammad Javad Zarif called it a "win-win outcome."
Those involved have spent 18 months in broader negotiations that were extended twice since an interim accord was reached shortly after Iranian President Hassan Rouhani entered office. That deal itself was the product of more than a year of secret negotiations between the Obama administration and Iran, a country the U.S. still considers the world's leading state sponsor of terrorism.
Opponents of the emerging accord, including Israel and Republican leaders in Congress, reacted with skepticism. They criticized the outline for failing to do enough to curb Iran's potential to produce nuclear weapons or to mandate intrusive enough inspections. Obama disagreed.
"This framework would cut off every pathway that Iran could take to develop a nuclear weapon," he declared. "This deal is not based on trust. It's based on unprecedented verification."
If implemented, the understandings reached Thursday would mark the first time in more than a decade of diplomatic efforts that Iran's nuclear efforts would be rolled back.
It commits Tehran to significant cuts in centrifuges, the machines that can spin uranium gas to levels used in nuclear warheads. Of the nearly 20,000 centrifuges Iran now has installed or running at its main enrichment site, the country would be allowed to operate just over 5,000. Much of its enriched stockpiles would be neutralized. A planned reactor would be reconstructed so it produced no weapons-grade plutonium. Monitoring and inspections by the U.N. nuclear agency would be enhanced.
America's negotiating partners in Europe strongly backed the result. President Francois Hollande of France, which had pushed the U.S. for a tougher stance, endorsed the accord while warning that "sanctions lifted can be re-established if the agreement is not applied."
Obama sought to frame the deal as a salve that reduces the chances of the combustible Middle East becoming even more unstable with the introduction of a nuclear-armed Iran. Many fear that would spark an arms race that could spiral out of control in a region rife with sectarian rivalry, terrorist threats and weak or failed states.
Obama said he had spoken with Saudi Arabia's King Salman and that he'd invite him and other Arab leaders to Camp David this spring to discuss security strategy. The Sunni majority Saudis have made veiled threats about creating their own nuclear program to counter Shia-led Iran.
The American leader also spoke by telephone with Israeli Prime Minister Benjamin Netanyahu, perhaps the sharpest critic of the diplomacy with Iran. Netanyahu told Obama a deal based on the agreement "would threaten the survival of Israel." The White House said Obama assured Netanyahu that the agreement would not diminish U.S. concerns about Iran's sponsorship of terrorism and threats toward Israel.
Obama saved his sharpest words for members of Congress who have threatened to either try to kill the agreement or approve new sanctions against Iran. Appearing in the Rose Garden, Obama said the issues at stake are "bigger than politics."
"These are matters of war and peace," he said, and if Congress kills the agreement "international unity will collapse, and the path to conflict will widen."
Hawks on Capitol Hill reacted slowly to the news from the Swiss city of Lausanne, perhaps because the framework was far more detailed than many diplomats had predicted over a topsy-turvy week of negotiation.
House Speaker John Boehner said it would be "naive to suggest the Iranian regime will not continue to use its nuclear program, and any economic relief, to further destabilize the region."
Senate Foreign Relations Committee Chairman Bob Corker, R-Tenn., said his panel would vote this month on legislation giving Congress the right to vote on a final deal. Freshman Sen. Tom Cotton, R-Ark., who penned a letter that many GOP senators signed last month to Iran's leaders, said he would work "to protect America from this very dangerous proposal."
Many of the nuclear limits on Iran would be in place for a decade, while others would last 15 or 20 years. Sanctions related to Iran's nuclear programs would be suspended by the U.S., the United Nations and the European Union after the International Atomic Energy Agency confirmed Iran's compliance.
In a joint statement, European Union foreign policy chief Federica Mogherini and Iran's Zarif called the agreement a "decisive step." Highlighting Iran's effort to show a new face of its government, Zarif then held a news conference, answering many questions in English, and Obama's statement was carried live and uncensored on Iranian state TV.
Still, all sides spoke with a sense of caution.
"We have taken a major step, but are still some way away from where we want to be," Zarif told reporters, even as he voiced hope that a final agreement might ease suspicion between the U.S. and Iran, which haven't had diplomatic relations since the 1979 overthrow of the shah and the subsequent U.S. Embassy hostage crisis in Tehran.
Zarif said the agreement would show "our program is exclusively peaceful, has always been and always will remain exclusively peaceful." But he also said it would not hinder the country's pursuit of atomic energy for civilian purposes. "We will continue enriching," he said. "We will continue research and development." He said the heavy water reactor would be "modernized."
Kerry lashed out at critics who have demanded that Iran halt all uranium enrichment and completely close a deeply buried underground facility that may be impervious to an air attack.
"Simply demanding that Iran capitulate makes a nice sound bite, but it is not a policy, it is not a realistic plan," Kerry said.
The final breakthrough came a day after a flurry of overnight sessions between Kerry and Zarif, and meetings involving the six powers at a luxury hotel in Lausanne.
As late as Thursday afternoon, it still appeared an agreement might be beyond reach as the U.S. pushed to spell out concrete commitments and Iran adamantly demanded that only a vague statement be presented. In an apparent compromise, some details were noted in the general statement and others were saved for a more detailed position paper issued by the White House and State Department.
Some of that tension remained.
"There is no need to spin using 'fact sheets' so early on," Zarif tweeted. He also questioned some of the assertions contained in the document, such as the speed of a U.S. sanctions drawdown.
Associated Press writers Julie Pace and Bradley Klapper contributed to this report from Washington.