The official, speaking on condition of anonymity, said on Monday that the powers are not "naive" about the difficulty of achieving such a deal
Six world powers - the United States, Russia, China, France, Britain and Germany - hold talks with Iran on its atom work in Geneva on Tuesday and Wednesday.
"No one should expect a breakthrough overnight," the American official noted.
The official also said Washington was ready to offer Iran rapid relief from economic sanctions if Tehran moved quickly to address concerns over Iran’s nuclear work.
Iran's Foreign Minister Mohammad Javad Zarif also said he hoped a "roadmap" could be reached, describing the process as "time-consuming".
Iran says it pursues the nuclear program under the International Atomic Energy Agency (IAEA) supervision to acquire nuclear energy for peaceful purposes.
NTJ/BA