The Obama administration is asking Congress to hold fire on enacting new sanctions against Iran, to give negotiators flexibility in current nuclear talks .
Even as US officials argue that tough sanctions are what brought Iran to the negotiating table in the first place, the White House and State Department said the administration wanted politicians to wait on new sanctions to give the negotiations time to get traction.
Some politicians have argued that now is not the time to ease pressure and that pursuing new sanctions will give the US additional leverage in the talks.
But State Department spokeswoman Jen Psaki said it was the consensus of the administration's national security teams that a pause "would be helpful in terms of providing some flexibility while we see if these negotiations will move forward".
She said the position was delivered to politicians and congressional aides at a White House meeting on Thursday.
"We have conveyed that any congressional action should be aligned with our negotiating strategy as we move forward. So while we understand that Congress may consider new sanctions, we think this is a time for a pause, as we asked for in the past, to see if negotiations can gain traction," Ms Psaki said.
She noted that additional sanctions could always be imposed later if the Iranians failed to meet their obligations and she stressed that no existing sanctions were being lifted.
At the White House, national security council spokeswoman Caitlin Hayden said the negotiations would not last indefinitely without progress and movement from Iran, which has long defied international demands to come clean about its nuclear intentions.
"The window for negotiation is not open-ended and if progress isn't made, there may be a time when more sanctions are, in fact, necessary," Ms Hayden said. "We have always said that there would be no agreement overnight, and we've been clear that this process is going to take some time."
Bi-partisan pressure in Congress to step up sanctions on Iran has been rising for some time and hit a new high last week after negotiators from the United States, the other four permanent members of the United Nations Security Council and Germany met Iranian officials in Geneva.
The chief US negotiator, Wendy Sherman, told Congress before those talks that the administration would support tougher sanctions on Iran if it did not come to the Geneva talks with "concrete, substantive actions" and a verifiable plan to scale back its nuclear programme.
The United States and other world powers fear Iran is trying to develop nuclear weapons. The Islamic republic says its programme is for peaceful energy production and this week's meetings in part focused on how to scale back its enrichment of material that can be used to generate power or nuclear warhead material.
The Senate Banking Committee is expected to draft new sanctions shortly after the government reopens, largely mirroring a House of Representatives bill that passed overwhelmingly by a 400-20 vote in July and blacklisted Iran's mining and construction sectors. It also called for all Iranian oil sales to end by 2015.
The Senate's bill may narrow that timeframe, block international investment in more economic sectors, try to close off Iran's foreign accounts and tighten Obama's ability to waive requirements for allies and key trading partners who continue to do business with Iran.