Former U.S. President Donald Trump withdrew from the deal in 2018, prompting Iran to steadily overstep the accord's limits on its nuclear program created to make it harder to develop an atomic bomb - an ambition Tehran denies. Tehran has rejected direct negotiations, and Washington said on Monday it expected the discussions to be hard. Neither side expected any early breakthrough.
Speaking from Tehran, Iranian government spokesman Ali Rabiei said Iran was neither optimistic nor pessimistic about the outcome of the meeting.
The remaining parties to the deal have met at a Viennese hotel for preparatory talks amid snowy conditions in the Austrian capital, where the pact was originally reached in 2015.
According to its foreign ministry, the main aim of Tuesday's talks for officials in Tehran is to determine "the path of lifting sanctions".
"Lifting U.S. sanctions is the first and the most necessary action for reviving the deal", Araghchi was quoted as saying.
Russian diplomat participating in talks to save 2015 JCPOA accord says meeting in Vienna has been "successful", though salvage efforts will take time. How long? Nobody knows. In exchange, sanctions were lifted by the United Nations, the US, and the other world powers who signed on - the United Kingdom, France, Germany, Russia and China.
The US delegation, headed by special envoy Rob Malley and sanctions expert Richard Nephew, are based in a nearby hotel.
"This is going to involve discussions about identifying the steps that the U.S. has to take and identifying the steps that Iran is going to have to take", Malley told NPR radio on Tuesday morning.
On the US side, there are questions around which sanctions the Biden administration will lift, after the Trump administration targeted hundreds of Iranian businesses, officials, economic sectors, and state-owned firms and agencies.
Iranian officials insist that meetings between the United States and other participants in the JCPOA do not involve them and do not amount to indirect negotiations between Washington and Tehran.
Since then, Iran has been steadily violating the restrictions of the deal, like the amount of enriched uranium it can stockpile and the purity to which it can enrich it. Tehran's moves have been calculated to put pressure on the other nations in the deal - Russia, China, France, Germany and Britain - to do more to offset crippling sanctions reimposed under Trump. Tehran has long denied it is enriching uranium for any other objective than civilian nuclear energy.
"The US has so far failed to honor @POTUS campaign promise to rejoin the JCPOA".
"But we do believe that these discussions with our partners, and in turn our partners with Iran, is a healthy step forward", he stated.
Ahead of Tuesday's talks, an Iranian prosecutor said 10 officials have been indicted over last year's military shooting-down of a Ukrainian passenger plane in which 176 people died.
Price said the talks will be "structured around working groups" that the European Union will form with Iran and the other parties to the deal.
But especially amid fierce pressure in Washington and from regional allies like Israel, a renewed nuclear deal would still leave a long road ahead for the Biden administration, which seeks to "lengthen and strengthen" the original agreement, including by addressing Iran's support for proxy forces across the region and its ballistic missile program.
Ali Shamkhani, the secretary of Iran's Supreme National Security Council, rejected on Tuesday the idea of any follow-on agreement.
They're prepared to grant billions and billions of dollars in sanctions relief and the question is how well are they going to be to really be willing to crack the whip and demand that the Iranians strengthen this deal as well as address some of their really malign activities that weren't part of this deal at all.