The U.S. State Department has confirmed that senior officials from the Iranian and U.S. governments have held direct talks on the sidelines of nuclear negotiations in Geneva.
The October 15 meeting, which lasted about an hour, was described by U.S. officials as "useful."
The talks included U.S. Undersecretary of State Wendy Sherman and Iranian Deputy Foreign Minister Abbas Araqchi.
Araqchi said before the meeting that it would only be normal to exchange opinions with U.S. officials.
Earlier in the day, after the start of two days of talks in Geneva
between senior officials from Iran and the 5+1 group of world powers, a spokesman for EU foreign policy chief Catherine Ashton said Iran had made a "very useful" presentation on how to resolve the dispute over its nuclear program, which many in the West suspect is aimed at developing nuclear weapons.
Ashton spokesman Michael Mann said the group was moderately hopeful about the outcome of the talks, adding, "We have come here with a sense of cautious optimism and a great sense of determination, because we believe it is really time now for tangible results."
Ashton is leading the 5+1 group, comprising the five permanent members of the UN Security Council -- the United States, Russia, China, Britain, and France -- plus Germany.
Mann told RFE/RL's Radio Farda that Iranian Foreign Minister Javad Zarif unveiled Tehran's proposal in a two-hour meeting, suggesting that Tehran had come to the talks with a detailed proposal.
Araqchi -- who is conducting the actual negotiations for Iran -- told journalists himself that world powers had a favorable reaction to Iran's plan, whose formal title is "An End to the Unnecessary Crisis and a Beginning for Fresh Horizons."
Araqchi said the Iranian plan "has the capacity to make a breakthrough." He gave no details of the proposals, describing them as "confidential."
However, Araqchi told Iran's ISNA news agency that any final agreement should eliminate sanctions and enable Iran to continue to enrich uranium. He also said Tehran's nuclear offer did not allow for unannounced snap inspections of its nuclear facilities by international monitors.
"The Guardian" newspaper reported that Iran's proposal is thought to lay out a timetable for confidence-building measures that would offer some limits on Tehran's nuclear program in exchange for relief from economic sanctions and recognition of its right to enrich uranium.
The talks are the most extensive since Iranian President Hassan Rohani took office in August with a pledge to try and resolve the decade-old nuclear standoff within six to 12 months.
Tehran has rejected previous international demands that it stop enriching uranium to the 20 percent level and ship out its stocks.
The six world powers want Iran to stop 20 percent enrichment because it is a short technical step away from weapons-grade enrichment.
Based on reporting by Reuters, dpa, AFP, ISNA, and RFE/RL's Radio Farda