White House press secretary Jay Carney on Thursday said the P5+1 group conducting talks with Iran on its nuclear program was weighing the possibility of easing some sanctions against Tehran to further advance negotiations.

Carney told reporters that “limited, targeted and reversible relief that does not alter our core sanctions architecture” could be offered in exchange for “concrete verifiable measures” on Iran’s part to rein in its nuclear program. He stressed that the measures would be "temporary" and that tougher sanctions could be reinstated if Tehran fails to act on its promises.

Reports earlier today said world powers were willing to halt some sanctions if Iran took steps to limit its nuclear program. The administration has launched a new round of talks with Iran after the election earlier this year of President Hassan Rouhani, who is seen as a moderate. Rouhani is seeking to undo international sanctions that have had a crippling effect on the country's economy.

Tehran insists that its nuclear program is for peaceful energy purposes, but the U.S. and key allies, including the European Union and Israel, fear Iran is building nuclear weapons.

Carney said that the P5+1 group, which consists of the U.S., United Kingdom, France, Germany, Russia and China, is engaged in “serious and substantial” negotiations.

He cautioned though that any relief from the sanctions regime would be part of a “phased approach” and linked to steps preventing Iran’s “nuclear program from moving forward and potentially rolling back parts of it.”

He added that sanctions would be “maintained until there is a final, verifiable agreement” and that any relief could be “terminated” if Iran fails to cooperate, or uphold its commitment to treaties and international bodies.

Carney said the “P5+1 remains united in this approach.”

But the White House effort faces opposition on Capitol Hill, where lawmakers may consider legislation to block the administration from easing any sanctions on Iran.

“No one is suggesting an open-ended delay to sanctions, for new sanctions,” Carney said in response to a question about congressional concerns. He added that there may come a point where additional sanctions were needed, but encouraged lawmakers to allow the U.S. to press forward in talks.