"We found the Iranian presentation very useful. The Iranian proposal was a new proposal with a level of seriousness and substance that we had not seen before," White House Press Secretary Jay Carney said at his news conference.
Carney said the discussions are continuing between the P-5+1 and Iran in Geneva.
"Yesterday, for the first time, the P-5 plus one and Iran had very technical discussions," he said, adding that the next round of talks would be held in Geneva next month.
"Having said that, no one should expect a breakthrough overnight. I mean, these are complicated issues, they're technical issues, and as the president has said, the history of mistrust is very deep."
"The onus remains on Iran to come into compliance with its international obligations, and any deal must prove to the international community that Iran's programme will be used for exclusively peaceful purposes," Carney insisted.