Former President Donald Trump withdrew from the accord in 2018, re-imposing strict USA sanctions on Iran's economy and government. "We don't anticipate an early or immediate breakthrough, as these discussions, we fully expect, will be hard". Neither side expected any early breakthrough.
Even without face-to-face talks, however, the presence of both Iran and the United States in the same location marks a step forward.
Iranian Foreign Minister Mohammad Javad Zarif in March also urged the U.S.to act quickly, noting that as his country's June elections approach, Washington will find itself dealing with a government unable to make progress in the nuclear talks.
The remaining parties to the deal briefly met at a Viennese hotel for preparatory talks in the Austrian capital, where the pact was originally reached in 2015.
"There's unity and ambition for a joint diplomatic process with two expert groups on nuclear implementation and sanctions lifting", he said.
The experts were set to begin technical work later on Tuesday with the aim of marrying lists of sanctions that the United States could lift with nuclear obligations Iran should meet.
"The lifting of USA sanctions is the first and most necessary step to re-establish the Joint Comprehensive Plan of Action". It will take some time. "How long? Nobody knows", he wrote.
The in-person meeting of the joint commission of the JCPOA was held in Vienna.
This came as Saudi Arabia requested to join the talks between Iran and Russia, China, Britain, France, and Germany in Vienna due to start today.
Russian Federation and China, the other parties to the 2015 pact, are also attending.
The US delegation, headed by special envoy Rob Malley, is based in a nearby hotel.
President Joe Biden was an instrumental player in the Obama administration that first struck the JCPOA in 2015 and has vowed to renegotiate the agreement.
Iranian officials insist that meetings between the USA and other participants in the JCPOA do not involve them and do not amount to indirect negotiations between Washington and Tehran.
"It is a potentially useful step as we seek to determine what it is that the Iranians are prepared to do to return to compliance with the stringent limitations under the 2015 deal and, as a result, what we might need to do to return to compliance ourselves", he added. There are critical questions remaining, including how quickly Iran can dismantle the advanced centrifuges now spinning, how it will reduce its stockpile of enriched uranium, and what to do about its gains in research and development as it violated its terms of the deal.
"The US has so far failed to honor @POTUS campaign promise to rejoin the JCPOA. There's unity and ambition for a joint diplomatic process with two expert groups on nuclear implementation and sanctions lifting", European Union chief coordinator Enrique Mora said on Twitter. "If US lifts all sanctions, Iran will then cease all remedial measures".
Iranian Supreme Leader Ayatollah Ali Khamenei, who has the final say on all state matters, has demanded sanctions be lifted all at once and rejected proposals that would lift them gradually.
Iran has called for Saudi Arabia to engage in direct talks to solve ongoing issues between the two countries without the involvement of a third party, Foreign Ministry spokesman Saeed Khatibzadeh said yesterday.
Speaking in florid propagandistic tones, Rabiyee said, "Today, we are at the beginning of a plan to revive the nuclear deal and the United States government has no choice but to end its law-breaking behavior and illegal sanctions".
The ultimate goal of the deal is to prevent Iran from developing a nuclear bomb, something it insists it doesn't want to do.
In late February, Iran began restricting worldwide inspections of its nuclear facilities, but under a last-minute deal worked out during a trip to Tehran by Rafael Grossi, the head of the Vienna-based United Nations atomic watchdog, some access was preserved.