In a two-hour, closed-door meeting at the White House, Obama provided the lawmakers, who serve on committees that deal with sanctions and foreign relations, with details about a proposal being discussed by world powers and Iran at talks this week in Geneva, spokesman Jay Carney.

"The president made clear that achieving a peaceful resolution that prevents Iran from obtaining a nuclear weapon is profoundly in America's national security interest," Carney said, stressing that it is Obama's obligation to try to achieve a diplomatic solution.

The five permanent members of the UN Security Council plus Germany (P5+1) have proposed a six-month deal that would see some sanctions eased in return for Iran halting progress on its nuclear programme while a final agreement is negotiated.

Obama warned the senators "that in the absence of a first step, Iran will continue to make progress on its nuclear programme," Carney said.

"We will see, in Geneva, whether or not Iran is prepared to reach an agreement with the unified P-5 plus one that commits itself to, in a transparent way, taking steps to halt progress on its nuclear program and roll back certain important aspects of it," Carney said.

Senator Bob Corker, the top Republican on the Senate Foreign Relations Committee, told reporters after the talks that he would consider Obama's request that Congress delay its push for tougher sanctions on Iran. Congress will recess next week for the Thanksgiving holiday, making it unlikely that new sanctions could be voted on quickly.