Obama Says Deal Offers Opportunity for 'New Direction' in Iran Ties

U.S. President Barack Obama lauded a landmark nuclear agreement with Iran as vindication of his diplomatic approach and a chance for a "new direction" in decades of vexed relations with Tehran.

Obama said the deal -- which would curb Iran's nuclear program in return for substantial international sanctions relief -- cut off "every pathway" to an Iranian atomic weapon.

"Today, because America negotiated from a position of strength and principle, we have stopped the spread of nuclear weapons in this region," he said in a White House address.

Describing a "difficult history" between Iran and the United States that "cannot be ignored," Obama shaped it as a diplomatic victory that showed "it is possible to change."

"This deal offers an opportunity to move in a new direction. We should seize it," he said.

Relations between the U.S. and Iran were smashed amid the tumult of the 1979 Islamic Revolution and the subsequent seizing of hostages at the U.S. embassy in Tehran.

Obama came to office vowing to talk directly to Tehran and to try to reach a negotiated deescalation -- a marked shift from his predecessor, who rejected a similar deal struck by European countries.

"This deal demonstrates that American diplomacy can bring real and meaningful change," he said.

But, he warned, if Iran steps back from measures agreed in the lengthy agreement, all sanctions "will snap back into place."

Obama insisted the alternative to diplomacy was more violence in a region already beset by instability.

"Put simply, no deal means a greater chance of more war in the Middle East," he said.

Firmly tethering his presidential legacy to Tuesday's deal, Obama had a further warning to domestic opponents.

He said it was "irresponsible" to walk away from the agreement and vowed to veto any effort in the Republican-controlled Congress to block it.

The prospect of better U.S.-Iran relations alarms Saudi Arabia and other Sunni-ruled Gulf Arab states, which are deeply suspicious of Shiite Iran and accuse it of stoking unrest in Syria, Yemen and elsewhere.

Reflecting the concerns, a senior U.S. official said Obama would soon speak to Israeli and Saudi leaders.

Israeli Prime Minister Benjamin Netanyahu on Tuesday called the deal "a historic mistake for the world."

"We will always defend ourselves," he added.

"We did commit to preventing Iran from acquiring nuclear weapons, and this commitment still stands," he added in what was seen as a thinly veiled threat of pre-emptive strikes against Iranian nuclear sites.

Diplomats have long warned the deal will not bring smooth waters.

Even if Iran allows intrusive monitoring of nuclear sites, its security services continue to back groups throughout the Middle East that Washington has linked to "terror" attacks.

Obama said the deal was based on verification, not trust, and noted that differences between the two countries were "real."

Analysts have also warned that Iran's leaders may need to toughen anti-American rhetoric to ensure the backing of regime hardliners angered at the prospect of a deal with a power they view as the "Great Satan."

Iran has been a thorn in the side of many recent U.S. presidents.

Jimmy Carter’s re-election bid was scuttled by the 444 day Iran hostage crisis, which was resolved days after he left office.

Ronald Reagan’s second term was hamstrung by the Iran-Contra scandal, which saw secret arms sales to Tehran in the hope of securing the release of U.S. hostages in Lebanon.

George W. Bush had his efforts to stabilize Iraq repeatedly scuppered by Shiite militias with close ties to Iran's powerful revolutionary guards corps.