European diplomats had urged Tehran to come back with “realistic proposals” after Iran's delegation last week made numerous demands that were deemed unacceptable by the other parties to the accord — Britain, China, France, Germany and Russia.
The United States withdrew from the agreement in 2018 under former U.S. President Donald Trump. His successor, Joe Biden, has indicated that Washington is willing to return, and American diplomats in Vienna are being briefed by other powers.
The Vienna accord, formally known as the Joint Comprehensive Plan of Action, was meant to rein in Tehran's nuclear program in return for loosening economic sanctions against Iran.
Following the U.S. decision to withdraw and reimpose sanctions, Iran has ramped up its nuclear program again by enriching uranium beyond the thresholds allowed in the agreement. Tehran has also restricted monitors from the U.N. atomic watchdog from accessing its nuclear facilities, raising concerns about what the country is doing behind closed doors.
U.S. State Department spokesman Ned Price said that “some of the thorny issues that confronted us in terms of potentially returning to the Joint Comprehensive Plan of Action were resolved or were on a pathway to resolution” in previous rounds of talks.
“It was our hope that we would find the Iranians returning to Vienna prepared to work on those remaining issues, building on the progress that had been made in (rounds) one through six,” he told reporters in Washington on Wednesday before the resumption of talks was announced. "That is not what we found. It is our hope that round eight proceeds differently.”
Russia’s top representative expressed hope that an agreement could eventually be reached.
Mikhail Ulyanov tweeted Thursday that contacts with the United States and Iran “prove that both sides are very serious” about reviving the deal, though he added that “their visions of relevant ways and means differ.”
“The task of the negotiators is to overcome these differences. It’s feasible in the light of unity of purpose,” he said.
Matthew Lee in Washington contributed to this report.