A senior U.S. State Department official, who spoke on condition of anonymity, told The New York Times Tuesday Tehran's three-step proposal prompted a serious discussion among members of the so-called P5-plus-1, the five permanent members of the U.N. Security Council plus Germany.
"For the first time, we had very detailed technical discussions," the official said.
Iranian Deputy Foreign Minister Abbas Araqchi said Iran's proposal indicates a major shift in the country's attitude and hoped the P5-plus-1 would also be able to change its attitude.
"Without a change in their attitude, it would be difficult to move forward," he said.
Iran and the P5-plus-1 are expected to issue a joint communique after the end of Wednesday's talks in Geneva, Tasnim news agency reported.
Iranian Foreign Minister Javad Zarif and European Union foreign policy chief Catherine Ashton were set to attend the last session of talks after a few hours of delay in the day's schedule, the news agency said.