According to Reuters, United States President, Barack Obama, hailed a step towards a "more hopeful world", with Iran's President, Hassan Rouhani, saying that it proved that "constructive engagement works". But Israel said it would do what it could to kill a deal that it called an "historic surrender".
The agreement will now be debated in the U.S. Congress, but Obama said he would veto any measure to block it. "This deal offers an opportunity to move in a new direction," Obama said. "We should seize it."
Under the deal, sanctions imposed by the United States, European Union and United Nations will be lifted in return for Iran agreeing long-term curbs on a nuclear program that the West has suspected was aimed at creating a nuclear bomb.
The agreement is a momentous political victory for both Obama, who has long promised to reach out to historic enemies, and Rouhani, a pragmatist elected two years ago on a vow to reduce the isolation of his nation of almost 80 million people.
Both leaders face scepticism from powerful hardliners at home, after decades of enmity between nations that referred to each other as "the Great Satan" and a member of the "Axis of Evil".
Rouhani was quick to present the deal as a step on the road towards a wider goal of international cooperation: "With this unnecessary crisis resolved, new horizons emerge with a focus on shared challenges," he tweeted.
For Obama, the diplomacy with Iran, begun in secret more than two years ago, ranks with his normalization of ties with Cuba as landmarks in a legacy of reconciliation with foes that tormented his predecessors for decades.
"History shows that America must lead not just with our might but with our principles," he said in a televised address. "Today's announcement marks one more chapter in our pursuit of a safer, more helpful and more hopeful world."
While the main negotiations were between the United States and Iran, the four other U.N. Security Council permanent members, Britain, China, France and Russia, are also parties to the deal, as is Germany.
Israeli Prime Minister, Benjamin Netanyahu, called the deal "a bad mistake of historic proportions". "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," he said. "Iran is going to receive a sure path to nuclear weapons."
His deputy foreign minister, Tzipi Hotovely, called the deal an "historic surrender" and said on Twitter that Israel would "act with all means to try and stop the agreement being ratified", a clear threat to try to use its influence to block it in the Republican-controlled U.S. Congress.
Congress has 60 days for a review, though if it rejects the deal, Obama can use his veto. It would require two-thirds of lawmakers to override such a veto, which means some of Obama's fellow Democrats would have to rebel against one of their president's signature achievements in order to kill the deal.
Republicans lined up against it. Presidential candidate Lindsey Graham, a senator from South Carolina, called it a terrible deal that would make matters worse.
Nor were hardliners silent in Iran: “Celebrating too early can send a bad signal to the enemy,” conservative lawmaker Alireza Zakani was quoted as saying in parliament by Fars News agency. Iran's National Security Council would review the accord, "and if they think it is against our national interests, we will not have a deal".