Negotiators were due to begin a new round of talks in Vienna on August 4 on salvaging a landmark 2015 nuclear accord between Iran and world powers.
The meeting would be the first one since March, when negotiations that began last year to reintegrate the United States into the agreement stalled.
Robert Malley, the U.S. special envoy for Iran, said on August 3 that he was headed to Vienna to resume the negotiations "with expectations in check."
The United States "is prepared for a good faith attempt to reach a deal," adding, "It will shortly be clear if Iran is prepared for the same."
Under the deal with the United States, Britain, France, Germany, Russia, and China, Iran pledged to curb its nuclear program in return for relief from economic sanctions.
But since Washington's unilateral pullout from the deal in 2018 under former President Donald Trump, Tehran has gradually broken from compliance with the accord.
In a last-ditch effort last month, the EU's top diplomat, Josep Borrell, submitted a compromise proposal and called on the parties to accept it to avoid a "dangerous nuclear crisis."
The European Union's lead coordinator for the indirect U.S.-Iranian talks to restore the agreement previously said the two sides were close to a deal before talks broke down in March.
Months of inaction and increased international isolation of Iranian ally Russia since the Kremlin attacked Ukraine in February have lowered hopes for a new deal that slowly emerged after another lull accompanying the election last year of hard-line Iranian President Ebrahim Raisi.
U.S. President Joe Biden's administration says it favors a return to the deal, including lifting key sanctions, but has rejected an Iranian demand to reverse the blacklisting of the Islamic Revolutionary Guards Corps as a terrorist organization.
Iran will be represented at the talks brokered by the European Union by chief nuclear negotiator Ali Bagheri Kani.
Russia's envoy to the talks, Mikhail Ulyanov, also tweeted about the return to negotiations.
Borrell said the draft text includes "hard-won compromises by all sides" and "addresses, in precise detail, the sanctions lifting as well as the nuclear steps needed to restore" the 2015 pact.
Rafael Grossi, the head of the UN nuclear watchdog, the International Atomic Energy Agency (IAEA), on August 2 warned Iran's program was "moving ahead very, very fast" and "growing in ambition and capacity."
On July 25, Iran said monitoring cameras belonging to the IAEA will not be turned back on until an agreement is reached.
