VIENNA (CBS News/CBSDC/AP) — 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 Barack 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.”

Obama said Iran’s path to a nuclear weapon has been “cut off.”

“I have no doubt 10 or 15 years from now the person who holds this office will be in a far stronger position with Iran further away from a weapon and with the inspections and transparancy that allow us to monitor the Iranian program. For this reason I believe it would be irresponsible to walk away from this deal,” Obama said.

The president stated that “no deal means a greater chance of more war in the Middle East.”

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“I have been president and commander in chief for over six years now. Time and again I have faced decisions about whether or not to use military force. It’s the gravest decision that any president has to make. Many times in multiple countries I have had to use force, and I will never hesitate to do so when it is in our national security interest,” Obama said. “I strongly believe that our national security interest now depends on preventing Iran from obtaining a nuclear weapon, which means that without a diplomatic resolution, either I or a future U.S. president would face a decision about whether or not to allow Iran to obtain a nuclear weapon or whether or not to use our military to stop it. But simply, no deal means a greater chance of more war in the Middle East. Moreover, we give nothing up by testing whether or not this problem can be solved peacefully.”

In a message to Congress, Obama said that he will “veto any legislation that prevents the successful implementation of this deal.”

“I welcome a robust debate in Congress on this issue, and I welcome scrutiny of the details of this agreement,” Obama said. “But I will remind Congress that you don’t make deals like this with your friends.”

Obama said that the deal “is not built on trust, it is built on verification.”

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.”

Israeli Prime Minister Benjamin Netanyahu called it a “historic mistake for the world.”

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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 essentials of the deal, including the removal of two thirds of Iran’s uranium enriching centrifuges — reducing their number from approximately 19,000 to 6,000 — the destruction of 98 percent of its stockpile of already-enriched uranium, and other elements, remain the same as what was in the previously-announced framework agreed in Lausanne, Switzerland in April.

In a nod to varying interpretations of that framework by Iran and U.S. officials to their respective constituencies, Zarif said Tuesday alongside Mogherini, as he prepared to read his statement in Farsi, “don’t worry, it’s the same.”

Iran will remain locked out of the U.S. financial system, and an existing U.S. ban on arms sales will continue. A separate U.N. ban on arms sales will be peeled back over time as Iran verifiably complies with the terms of the agreement.

U.N. Secretary-General Ban Ki-moon said in a statement that he hoped, “and indeed believe – that this agreement will lead to greater mutual understanding and cooperation on the many serious security challenges in the Middle East. As such it could serve as a vital contribution to peace and stability both in the region and beyond.”

A senior Iranian official called it an “historic day,” and Iranian President Hassan Rouhani took to Twitter to laud the deal as the beginning of a new era “with a focus on shared challenges.”

Rouhani called it “a new chapter in history” and a “victory” for Iran.

#IranDeal shows constructive engagement works. With this unnecessary crisis resolved, new horizons emerge with a focus on shared challenges. — Hassan Rouhani (@HassanRouhani) July 14, 2015

I'm pleased to announce that after 23 months of negotiations this admin managed to reach a new point, a new chapter in history #IranDeal. — Hassan Rouhani (@HassanRouhani) July 14, 2015

The steadfastness, resistance, patience, perseverance & support of the great nation of #Iran were indeed key to this victory. #IranDeal — Hassan Rouhani (@HassanRouhani) July 14, 2015

In a separate deal, the head of Iran’s atomic program signed an agreement with the International Atomic Energy Agency, the U.N. nuclear watchdog, to take steps to resolve outstanding questions about the country’s past research into weapons development and to allow additional inspectors ‎into the country.

IAEA chief Yukiya Amano told reporters the “roadmap” agreed to with the Iranians would “enable the agency, with the cooperation of Iran, to make an assessment of issues relating to possible military dimensions to Iran’s nuclear program by the end of 2015. It sets out a clear sequence of activities over the coming months including a provision by Iran of explanations regarding outstanding issues.”

Prior to the announcement, a senior diplomat told the Associated Press that the deal included a compromise between Washington and Tehran that would allow U.N. inspectors to press for visits to Iranian military sites as part of their monitoring duties.

But access at will to any site would not necessarily be granted and even if so, could be delayed, a condition that critics of the deal are sure to seize on as possibly giving Tehran time to cover any sign of non-compliance with its commitments.

The U.S. Congress will have 60 days to review the terms agreed to in Vienna, after which they will vote on the pact. There has been fierce opposition to the deal, even before the details were known, from many Republicans and some Democrats in Washington, and they may try to block implimentation of the measures with their votes. Congress does not have the power, however, to completely obstruct the agreement reached by the executive branch with other nations.

Opposition to the deal has also been fierce from Israel, the most entrenched U.S. ally in the Middle East.

Prime Minister Benjamin Netanyahu called the deal a “bad mistake of historic proportions” on Tuesday, adding that it would enable Iran to “continue to pursue its aggression and terror in the region.”

Under the deal, Tehran would have the right to challenge the U.N request and an arbitration board composed of Iran and the six world powers that negotiated with it would have to decide on the issue.

Still, such an arrangement would be a notable departure from assertions by top Iranian officials that their country would never allow the U.N’s International Atomic Energy Agency into such sites. Iran has argued that such visits by the IAEA would be a cover for spying on its military secrets.

The accord will “grant Tehran sanctions relief in exchange for curbs on its nuclear program,” the Reuters news agency quotes an Iranian diplomat as saying Tuesday.

“All the hard work has paid off and we sealed a deal. God bless our people,” the diplomat told Reuters on condition of anonymity. Another Iranian official confirmed the agreement to Reuters.

The news agency also reports that “Iran has accepted a so-called ‘snapback’ plan that will restore sanctions in 65 days if it violates” the deal.

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