News reports say the Obama administration is considering gradually unfreezing some of Iran's overseas funds to ease the pain of sanctions aimed at curbing the country's nuclear program.
The proposal would reportedly free up Iran's assets in installments.
The reports - citing unnamed senior administration officials - come after talks in Geneva this week over Iran's disputed nuclear program that White House spokesman Jay Carney said showed "a level of seriousness and substance" from Iran that has not been seen before.
But White House spokeswoman Bernadette Meehan said that discussion of specific types of sanctions relief was "premature and speculative." She said Iran would have to agree to what she described as "meaningful, transparent, and verifiable actions" before the U.S. can seriously consider taking steps to ease sanctions.
Iran insists its nuclear program is peaceful, but the United States and other world powers want Tehran to prove it is not aiming toward developing nuclear weapons.
The Geneva talks were held between Iran and the group known as the P5+1, which includes the five permanent members of the United Nations Security Council -- the U.S., Russia, China, France and Britain -- plus Germany. The group meets with Iran again in three weeks.
The P5+1 has demanded Iran suspend uranium enrichment or ship its stockpiles of processed uranium abroad. The group also wants Iran to comply with a comprehensive verification regime including unannounced checks by U.N. inspectors.
The Geneva talks are the first since Iran's new president, relative moderate Hassan Rouhani, was elected in June. He promised to lead a diplomatic effort to get economic sanctions against Iran eased, but P5+1 officials have said Iran must prove its sincerity through concrete steps before that will happen.
U.S. Senator Marco Rubio has sought to keep pressure on Iran by introducing a non-binding resolution calling on Congress to adopt further sanctions if Iran does not give up its nuclear program. He said in a statement that Iran has "broken its word far too many times to be trusted."
Rubio's action follows a group of 10 senators who sent a letter to President Barack Obama earlier this week saying they are open to suspending any new sanctions if Iran takes significant steps.
Israel, meanwhile, has warned against easing the pressure on Iran, with Prime Minister Benjamin Netanyahu saying it would be a "historic mistake."