After 18 days of intense negotiations, the U.S. and five other world powers have reached a deal to freeze Iran's nuclear program for the next decade in exchange for gradual sanctions relief that rolls out as Iran complies with a multi-step process.
The accord will keep Iran from producing enough material for a nuclear weapon for at least 10 years and impose new provisions for inspections of Iranian facilities, including military sites. And it marks a dramatic break from decades of animosity between the United States and Iran, countries that alternatively call each other the "leading state sponsor of terrorism" and the "the Great Satan."
Touting the deal in an early morning news conference from the White House, President Obama said one of the greatest dangers facing the U.S. today was the "risk is that nuclear weapons swill spread to more and more countries, particularly in the Middle East, the most volatile region in our world."
"We have stopped the spread of nuclear weapons in this region," declared Mr. Obama, insisting that, in spite of concerns over Iran's trustworthiness, the "international community will be able to verify that the Islamic Republic of Iran will not be able to develop a nuclear weapon... Every pathway to a nuclear weapon is cut off."
President Obama stressed there would be "very real consequences for a violation" of the agreement by Iran, and warned opponents in the U.S. and Israel that without the agreement there "would be no lasting constraints on Iran's nuclear program."
"This is a historic moment," Iranian Foreign Minister Mohammad Javad Zarif said as he attended a final session alongside his counterparts from the so-called P5+1; the United States, Britain, China, France, Germany and Russia, in Vienna on Tuesday morning. "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, confirmed in a tweet from European Union foreign policy chief Federica Mogherini which was promptly retweeted by U.S. Secretary of State John Kerry and his Iranian counterpart, will become binding once it is enshrined in an already-written United Nations Security Council resolution.
"Despite all the twists and turns in the talks and a number of extensions, hope and determination enabled us to overcome all the difficult moments," said Mogherini, officially announcing the agreement on the Joint Comprehensive Plan of Action.
She said the deal ensured that Iran's nuclear program would "exclusively be peaceful," and that the agreement marked "a shift" in the Iranians' approach to its atomic work.
"What we are announcing today is not only a deal, it is a good deal," proclaimed Mogherini, saying that "under no circumstances" would Iran be able to seek or acquire any nuclear weapons under the terms agreed to.
The economic and financial sanctions -- including a U.S. and European Union oil embargo -- will be lifted as Iran complies with the terms of the deal and as U.N. weapons inspectors verify their compliance.
The Associated Press contributed to this report.