LAUSANNE, SWITZERLAND |Thu Apr 2, 2015 7:01pm EDT

Iran and world powers reached a framework agreement on Thursday on curbing Iran's nuclear program for at least a decade, a step toward a comprehensive accord that could end 12 years of brinkmanship, threats and confrontation.

The tentative agreement, after eight days of marathon talks in Switzerland, clears the way for talks on the future settlement that should allay Western fears that Iran was seeking to build an atomic bomb and in return lift economic sanctions on the Islamic Republic.

The framework is contingent on reaching an agreement by June 30 and all sanctions onIran remain in place until a final deal is reached.

Many details still need to be worked out and diplomats close to the negotiations said the deal was fragile. It could not be ruled out that the understandings reached could collapse between now and June 30. Experts believe it will be much harder to reach a final deal that it was to agree the framework accord.

U.S. President Barack Obama said the outcome was a good deal, comparing it to nuclear arms control deals struck by his predecessors with the Soviet Union that "made our world safer" during the Cold War.

"Today, the United States, together with our allies and partners, has reached an historic understanding with Iran, which if fully implemented, will prevent it from obtaining a nuclear weapon," he declared.

Under the outline deal, Iran would shut down more than two-thirds of its installed centrifuges capable of producing uranium that could be used to build a bomb, dismantle a reactor that could produce plutonium, and accept intrusive verification.

The negotiations went right down to the wire, with no certainty that they would not end in failure.