Iran and six world powers clinched a deal on Sunday curbing the Iranian nuclear program in exchange for initial sanctions relief, signaling the start of a game-changing rapprochement that would reduce the risk of a wider Middle East war.
Aimed at easing a long festering standoff, the interim pact between Iran and the United States, France, Germany, Britain, China and Russia won the critical endorsement of Iranian clerical Supreme Leader Ayatollah Ali Khamenei.
President Barack Obama said the deal struck after marathon, tortuous and politically charged negotiations cut off Tehran's possible routes to a nuclear bomb.
But Israel, Iran's arch-enemy a U.S. ally, denounced the agreement as an "historic mistake". Critics in the U.S. Congress were quick to voice concern, with some raising the specter of failure to rein in North Korea on its nuclear programs, but they signaled that Congress would likely give the deal a chance to work.
The agreement, which halts Iran's most sensitive nuclear activity, its higher-grade enrichment of uranium, was tailored as a package of confidence-building steps towards reducing decades of tension and ultimately creating a more stable, secure Middle East.
Indeed, the United States held previously undisclosed, separate direct talks with Iran in recent months to encourage diplomacy towards a nuclear deal, a senior U.S. official said.
Washington and Tehran have not had diplomatic relations since the Iran's 1979 Islamic Revolution. Any new detente between the two will be opposed by Washington's Israeli and conservative Gulf Arab allies as it could tilt the regional balance of power towards Tehran.
European Union foreign policy chief Catherine Ashton, who has been coordinating diplomatic contacts with Iran on behalf of the major powers, said the accord created time and space for follow-up talks on a comprehensive solution to the dispute.
"This is only a first step," said Iranian Foreign Minister and chief negotiator Mohammad Javad Zarif. "We need to start moving in the direction of restoring confidence, a direction which we have managed to move against in the past."
Zarif said later in an interview broadcast on state television that Iran would move quickly to start implementing the agreement and it was ready to begin talks on a final accord.