VIENNA — The United States and five other world powers secured a deal with Iran on Tuesday morning to curtail its ability to build a nuclear weapon in return for lifting crippling economic sanctions, overcoming decades of distrust and concluding nearly two years of tense negotiations that were capped by a marathon diplomatic finale that lasted 18 days.
The 109-page agreement aims to remove a threat to regional stability in the Middle East, seeking to solve one of the region’s most enduring problems by drawing Iran into greater international cooperation.
The deal will go down as one of the most defining moments of President Obama’s foreign policy legacy by reshaping the relationship with an avowed American adversary in the Middle East. It will also be one of the signature accomplishments of the long career of Secretary of State John Kerry, who secured the accord despite deep skepticism, frequent criticism, and, even in the final weeks, a broken leg.
Kerry laid the foundation for new talks with Iran three and a half years ago while still a US senator from Massachusetts and displayed a dogged determination to finally see the investment of time and patience pay off following at least 58 negotiating meetings inside a 19th-century palace in the Austrian capital.
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“No deal means a greater chance for more war in the Middle East,” Obama said Tuesday at the White House. “It would be irresponsible to walk away from this deal.”
The agreement will now be presented to Congress, which will have 60 days to review and vote on it before the terms begin to be locked into place.
It would be difficult for congressional opponents to scuttle the deal. They would need at least a two-thirds majority to pass a disapproval resolution that could override a presidential veto. But on an issue of such significance, the Obama administration is hoping to demonstrate broad support.
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Even before the full details were known, Prime Minister Benjamin Netanyahu of Israel, a persistent critic of the talks, blasted the accord, saying it was “a bad mistake of historic proportions.”
“Iran is going to receive a sure path to nuclear weapons,” Netanyahu said in Jerusalem. “Many of the restrictions that were supposed to prevent it from getting there will be lifted. Iran will get a jackpot, a cash bonanza of hundreds of billions of dollars, which will enable it to continue to pursue its aggression and terror in the region and in the world.”
The pact was striking in that it was forged by two avowed adversaries who have barely spoken since Iran seized the American embassy in Tehran in 1979 and held 52 hostages for 444 days. Thirteen years ago, President George W. Bush labeled Iran one of three countries in the “axis of evil.”
Iranian leaders still refer to the United States as “the Great Satan.”
The agreement is intended to prevent Iran from producing enough nuclear material to build a nuclear weapon for 10 years and will also force Iran to submit to a series of enhanced inspections to ensure that it abides by the terms of the deal.
But one of the last hurdles — and one that is bound to spark opposition — is that a United Nations arms embargo would be lifted within five years for conventional weapons and eight years for ballistic weapons. The embargo could be lifted even sooner if Iran is able to prove to international inspectors that it doesn’t have any covert nuclear materials.
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The United States had opposed lifting the embargo.
Sanctions will start to be lifted as soon as Iran proves it has met the requirements for increased monitoring and that it dismantled some of its nuclear infrastructure. At that point, the vast majority of sanctions that have been imposed on Iran would be lifted, bringing in hundreds of billions of dollars in fresh revenue from sales of oil and the unfreezing of foreign-held Iranian assets.
“This is a historic moment,” Foreign Minister Mohammad Javad Zarif of Iran said as he attended a final session with negotiators, which in addition to the United States and Iran included Britain, China, Germany, France, and Russia. “We are reaching an agreement that is not perfect for anybody, but it is what we could accomplish, and it is an important achievement for all of us. Today could have been the end of hope on this issue. But now we are starting a new chapter of hope.”
The agreement came after officials spent most of the day Monday undergoing what all sides agreed would be their last round of negotiations. Around 10:30 p.m., Kerry and several of his negotiating partners met with Zarif for about 30 minutes. When they emerged, they told everyone they believed they had reached an understanding.
“People were pretty tired,” a senior administration official said. “There wasn’t this triumphant celebration with rounds of applause and things like that.”
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Kerry grew reflective Tuesday as he emotionally recounted serving in the Vietnam War just after college. He said he vowed then, if given the opportunity, he would do everything within his power to prevent war. “I learned in war the price that is paid when diplomacy fails,” he said.
Earlier, when addressing the other negotiating teams in a private meeting, Kerry gave a similar message, at one point choking up. When he finished, the whole room, including Iranians, applauded, a State Department official said.
The historic accord will provide inspectors from the International Atomic Energy Agency with enhanced access to review Iran’s nuclear-related activities.
Iran had earlier agreed to reduce its number of centrifuges by two-thirds — from 19,000 to 6,104 — and will also have to reduce its stockpiles of uranium. Those restrictions mean it would take Iran about a year to make a nuclear weapon — compared with about two months now — according to estimates from US officials.
Iran is also expected to adopt the so-called Additional Protocol, a UN statute that subjects it to more intrusive inspections and could allow officials to detect Iranian efforts to build a bomb.
International inspectors would have access to military sites if needed. If Iran denies access, sanctions could fall back into place.
Administration officials have stepped back from the idea that there would be access to Iran’s nuclear sites “anytime, anywhere,” as some had declared previously.
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“We don’t think that anytime, anywhere inspections are feasible,” a senior administration official said. “It’s just not something that happens anywhere in the world. While it’s a nice thing to say, it simply doesn’t exist.”
One of the most difficult issues to resolve was how and when to relieve sanctions — actions expected to pump tens of billions of dollars into the Iranian economy. Under the accord, American sanctions that date back to the 1979 Iranian revolution, when American diplomats were taken hostage in Tehran, would be removed. Importing of all goods, including oil, have been banned. A variety of global sanctions, in place since 2006 when Iran was found out of compliance with IAEA safeguards, would also be lifted.
One of the biggest boons to Iran will be allowing the country to further open its oil-rich country to the international market. Frozen foreign accounts and sanctions against Iranian banks have also isolated the country’s financial system. Iran would remain on the list of state sponsors of terrorism, however, and sanctions related to its support for terrorism and human rights violations would remain in place.
The agreement caps more than two weeks of furious negotiating and several missed deadlines.
Kerry met with his Iranian counterpart, Zarif, almost every day for several hours. Energy Secretary Ernest Moniz repeatedly met with his counterpart, Ali Akbar Salehi, with the two scientists, who have ties to MIT, chiseling away at some of the most technical details.
While the talks centered on Iran’s nuclear program, top officials on both sides believe a deal could be a game-changing development in the Middle East. Americans haven’t had any relationship with the Iranians, and if a trusting one develops, it could mean cooperation on other issues — possibly even on fighting the Islamic State.
One unclear aspect was the fate of several Americans held in Iran, including Washington Post reporter Jason Rezaian. While those held might not have been part of formal talks, senior administration officials would not say whether there was an informal arrangement or whether their release would be seen as a good-will gesture.
Kerry on Tuesday again called on Iran to release the American citizens it has detained.
More on the Iran nuclear deal:
Matt Viser can be reached at matt.viser@globe.com. Follow him on Twitter @mviser.