“We're asking you to give our negotiators and our experts the time and space to negotiate,” he said.
Some members of Congress have been skeptical of the temporary agreement reached between Iran and the five members of the UN Security Council plus Germany in Geneva last month because it allows Iran to continue to enrich uranium.
Kerry said America's negotiating partners - Russia, China, France, Great Britain and Germany - could back away from the deal “if we appear to be going off on a tangent.”
The top US diplomat, who was present at the negotiating sessions in Geneva, reiterated that the goal of the current deal was to set the stage for a comprehensive, long-term agreement that would resolve the decade-old dispute with Iran over its nuclear energy program.
The House of Representatives passed tougher sanctions against Iran in July, and the Senate is considering new sanctions legislation that would go into effect after the interim deal expires.
The Geneva accord, however, obligates the United States not to impose new sanctions during the six-month period of the deal.
“This is very delicate diplomatic moment. … We have an obligation to give these negotiations a chance to succeed,” Kerry told lawmakers.
There is little time for Congress to act on new sanctions with the House finishing work for the year on Friday and the Senate adjourning after next week.
Before Kerry’s testimony on Capitol Hill, key senators said it was unlikely Congress would approve new sanctions this year.
“I'm inclined to support John Kerry,” Senate Banking Committee Chairman Tim Johnson (D-S.D.) told The Hill. “We'll see. Not this year.”
Disappointed with the banking panel, hawkish senators were instead hoping to push for new sanctions as an amendment to the pending Defense Authorization Act.
Leaders of the House and Senate Armed Services committees, however, dashed the senators' hopes on Monday when they unveiled a join bill with no sanctions attached and called for a quick vote.
Meanwhile, Iran has warned that the interim nuclear deal it signed with world powers will be “dead” if the US imposes more sanctions against the country.
“The entire deal is dead. We do not like to negotiate under duress,” Mohammad Javad Zarif said in an interview with Time magazine in Tehran on Saturday, which was published on Monday.
“And if Congress adopts sanctions, it shows lack of seriousness and lack of a desire to achieve a resolution on the part of the United States,” he added.
Iran deal 'unequivocally' serves US interests, Kerry tells lawmakers
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