"No deal means a greater chance of more war in the Middle East," Obama said in early morning remarks from the White House.
Obama, accompanied by Vice President Joe Biden, spoke shortly after negotiators in Vienna announced the landmark deal aimed at curbing Iran's nuclear program for more than a decade in exchange for billions of dollars in international sanctions relief.
The president said the agreement, hammered out through nearly two years of negotiations, would cut off all of Iran's pathways to a bomb and give the international community unprecedented access to the country's nuclear facilities.
"This deal is not built on trust," Obama said. "It is built on verification."
For Obama, the accord marks the fulfillment of one of his top foreign policy goals and will be cast by the White House as a validation of the president's focus on seeking resolutions through diplomacy.
The president staked enormous political capital on the diplomatic pursuit with Iran, deeply straining relations with Israel and sparking outrage from some congressional lawmakers.
It will likely be well after Obama has left the White House before it is known whether the deal succeeds in preventing Iran from building a bomb. Critics say Iran cannot be trusted even with the lower levels of nuclear technology it will be allowed to retain under the terms of the agreement.
With the deal between the world powers now finalized, Congress has 60 days to assess the accord and decide whether to pursue legislation imposing new sanctions on Iran or prevent Obama from suspending existing ones. Obama called congressional leaders Monday night to alert them that a deal was at hand.
In his remarks Tuesday, the president renewed his vow to veto any such legislation and urged lawmakers to consider the repercussions of their actions. He painted a grim scenario in which the rest of the world struck its own nuclear deals with Iran, leaving the U.S. isolated. And without the limitations and verifications included in the deal announced Tuesday, Obama said he or a future U.S. president would be more likely to face a decision about using U.S. military action to prevent Iran from building a bomb.
In addition to his calls with congressional lawmakers, administration officials said Obama was likely to speak Tuesday with Israeli Prime Minister Benjamin Netanyahu, Saudi Arabia's King Salman, and European leaders.
Obama acknowledged Tuesday that the U.S. and Iran remain at odds over many issues, including Tehran's support for terrorism in the Middle East and its detention of several American citizens. Still, he suggested a breakthrough on the nuclear issue could pave the way for a broader shift in relations between the U.S. and Iran.
"This deal offers an opportunity to move in a new direction," Obama said. "We should seize it."