Nuclear talks towards a final agreement between Iran and six powers appeared to make modest progress on a second day Wednesday, with Washington saying the negotiations were "constructive and useful," according to AFP.
Iranian state media said both sides were close to agreeing a framework agreement on how negotiations would proceed in future rounds over the coming months.
U.S. State Department spokeswoman Marie Harf said that the Vienna talks between Iran and the United States, Russia, China, Britain, France and Germany had been "constructive and useful."
Negotiators discussed "both process and substance," she said, according to AFP.
Speaking to reporters, Harf declined to comment further, saying only that the talks would continue for a third day in the Austrian capital on Thursday.
Iranian Foreign Minister Mohammad Javad Zarif and EU foreign policy chief Catherine Ashton, the powers' chief negotiator, were expected to hold a closing news conference on Thursday morning, the news agency reported.
After years of talks, Iran and the six world powers, known as the P5+1, reached a six-month interim nuclear deal in November. That deal went into effect on January 20.
Under the agreement, Iran committed to limit its uranium enrichment to five percent, halting production of 20 percent-enriched uranium. In return, the European Union and the United States have eased crippling economic sanctions on Iran.
The parties hope to create a lasting accord out of the interim deal, which expires on July 20 but can be extended, with the parties aiming to conclude negotiations and implement the final "comprehensive" deal by November.
Zarif had said late Tuesday that the talks had "started on the right track."
"We have a shared objective, and that is for Iran to have a nuclear program that is exclusively peaceful," he said, according to AFP.
Zarif added that a deal was "totally achievable" but would take more than "one or two sittings" and would require "some innovation and some forward thinking."
Ahead of the talks, a senior U.S. official said getting to a deal would be a "complicated, difficult and lengthy process."
Iran's Supreme Leader Ayatollah Ali Khamenei also said he was not optimistic that the talks would lead to an agreement.
Even after the interim deal was reached, Iran has consistently said that it will not stop its nuclear program, which it claims is for peaceful purposes.
Several weeks ago, Zarif denied that his country had agreed to dismantle its centrifuges as part of the nuclear agreement.
He insisted that the Obama administration was mischaracterizing the concessions by Iran in the six-month nuclear deal, saying that "we did not agree to dismantle anything."
Iranian President Hassan Rouhani recently declared that his country will not dismantle its nuclear facilities.
Rouhani said nuclear weapons had no place in Iran’s defense strategy but also made clear that Tehran was determined to maintain a uranium enrichment program for peaceful purposes.