Kerry said the negotiators should have a 'few weeks' more to see if they can reach an agreement.
The request faces sharp resistance from members of Congress determined to further squeeze the Iranian economy and wary of yielding any ground to Iran in the talks.
"The Iranian regime hasn't paused its nuclear program," said Rep. Ed Royce, a Republican and House Foreign Affairs Committee chairman. "Why should we pause our sanctions efforts as the administration is pressuring Congress to do?"
Kerry said the potential accord with Iran relates to a "tough proposal," adding: If it weren't strong, why wouldn't Iran have accepted it yet?'
Kerry said," What we are asking everyone to do is calm down, look hard at what can be achieved and what the realities are. If this doesn't work, we reserve the right to dial back the sanctions. I will be up here on the Hill asking for increased sanctions, and we always reserve the military option. So we lose absolutely nothing, except for getting in the way of diplomacy and letting it work."
"We ought to be actually ratcheting up the sanctions against Iran," Republican Senate Minority Leader Mitch McConnell. "What the administration was promoting is something the Israelis think is a bad deal for them. It's pretty clear the Sunni Arab allies of ours also think it's a bad deal. Looking at it strictly from an American point of view, I think it's a bad deal as well."
Last week's talks broke down as Iran demanded formal recognition of what it calls its right to enrich uranium, and as France sought stricter limits on Iran's ability to make nuclear fuel and on its heavy water reactor to produce plutonium, diplomats said
President Barack Obama spoke Wednesday by telephone with French President Francois Hollande. The two countries "are in full agreement" on Iran, the White House said in a statement.
Obama is under pressure at home and abroad to resolve the Iran nuclear standoff, having said the U.S. has until sometime next year before the Islamic republic could reach nuclear weapons capacity. Obama has reached out in an unprecedented manner to Iran's new President Hassan Rouhani, with the two men holding the first direct conversation between U.S. and Iranian leaders in more than three decades.
At the same time, Obama has angered U.S. allies Israel and Saudi Arabia, which see an Iranian nuclear arsenal as existential threats.
The new sanctions were overwhelmingly approved by the Republican-led House in July. The legislation blacklisted Iran's mining and construction sectors and committed the U.S. to the goal of eliminating all Iranian oil exports worldwide by 2015. If the Senate Banking Committee pushes off its parallel bill any longer, lawmakers could attach it to a Senate defense bill which could come up for debate as early as Thursday.
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Associated Press writer Bradley Klapper contributed to this report.