Iran and world powers edged closer to breaking the decadelong stalemate over its nuclear program, saying an initial accord is possible when they convene for a second day of negotiations in Geneva.

Secretary of State John Kerry plans to visit the Swiss city to help narrow differences in the talks, according to a U.S. official. A framework has been agreed on and negotiators will try to fill in details at 's session, Iranian Foreign Minister Mohammad Javad Zarif said in an interview.

"Our job now is to test how serious they are about resolving this conflict, or this dispute, through peaceful means, through diplomacy," President Barack Obama said in an interview with NBC News. "We don't have to trust them. What we have to do is to make sure that there is a good deal in place from the perspective of us verifying what they're doing."

Iran has been offered "limited, targeted and reversible relief" from sanctions in return for concrete and verifiable concessions on its nuclear work, White House spokesman Jay Carney said in Washington.

Zarif said any concessions Iran makes at this stage will be reversible if there's no reciprocal move from the United States. He called on Obama to resist pressure for additional sanctions in Congress, where legislators were deciding whether to introduce a measure to tighten the curbs.

The accord sought in Geneva would be intended as a first step toward a comprehensive deal to remove the specter of another Middle East war.

The United States and Israel say they're willing to use force to stop Iran getting nuclear bombs, which it denies seeking. Hassan Rouhani's election as Iran's president in June and his pledge to restore an economy squeezed by sanctions has boosted to diplomacy.

Iran has signaled it's willing to make compromises, shelving a demand for immediate recognition that it has the right to enrich uranium, and saying it may be ready to limit its stockpile of uranium enriched to 20 percent purity.

But Israeli Prime Minister Benjamin Netanyahu said that any deal easing the pressure on Iran would be "a mistake of historic proportions."

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