The White House on Friday declined to renew its previous prediction that a Senate bill slapping new sanctions on Iran, which it fears could scupper nuclear talks, would not pass the Senate.
President Barack Obama's spokesman Jay Carney warned however that the bill would be detrimental to the drive to resolve the nuclear showdown with Tehran short of war.
"I think that we remain hopeful that Congress will not pass such a sanctions bill because of the negative effect that would have on the ongoing negotiations and the potential to resolve this peacefully," Carney said.
"But I'm not going to make legislative predictions."
Carney's comments appeared to hint at an eroding of the administration's position on the bipartisan legislation since December, when Carney threatened Obama would veto the bill if it passed.
"We don't think it will be enacted. If it were enacted, the president would veto it," Carney said of the legislation on December 19.
According to Senate procedure, a bill technically becomes an Act when it has passed one chamber of Congress. But it does not become law until the president signs it or until both the House of Representatives and the Senate have produced the necessary two-thirds vote to override a veto.
Obama and senior aides have repeatedly urged a bipartisan group of senators not to pass more sanctions on Iran, fearing they could undermine Tehran's negotiating team with conservatives back home and prompt Tehran to walk away from the table.
Lawmakers who support the bill say tough sanctions brought Iran to the negotiating table and stiffer measures would increase Obama's leverage in talks between the Islamic Republic and the P5+1 group of world powers.
The latest wrangling over sanctions in Washington came as negotiators agreed on how to implement a six-month interim deal on curtailing Iran's nuclear program in the latest round of talks in Geneva.
The deal will now be sent to respective capitals before it can be put into force.