State Department spokeswoman Jen Psaki said she hoped Reid would give world powers "the space they need" for future negotiations as well. The administration says any new sanctions right now could scuttle the diplomatic effort.
Several Democrat and Republican senators have voiced displeasure with the parameters of a potential agreement, arguing that the U.S. and its partners are offering too much for Iranian action that stops short of a full freeze on uranium enrichment.
On Thursday, the Republicans' top member of the Senate Foreign Relations Committee proposed a bill mapping out what a final agreement should look like and seeking to restrict Obama's capacity to offer sanctions relief.
"Many of us have concerns that an interim agreement in Geneva will diminish U.S. leverage without Iran meeting its existing international obligations," Sen. Bob Corker said.
The legislation gives Obama 240 days to conclude the deal and says he can only suspend restrictions on Iran if he certifies that such action advances U.S. national security interests and that Iran is fully complying with existing agreements. It says any final agreement must compel Iran to end all uranium enrichment activity, a condition the Islamic republic has steadfastly rejected and one which U.S. negotiators have long conceded.
The State Department's Psaki said no one would agree to a final pact that "does not address the big issues" of Iran's enriched uranium stockpiles and plutonium production and the need for greater inspections. But any indication right now that the United States isn't committed to diplomacy would be "unhelpful," she warned.