The dispute has been going on for months about who should take the first step towards reviving the 2015 nuclear deal.
Now the United States and Iran are engaged in indirect talks in Vienna, Austria while representatives from six other signatories of the Joint Comprehensive Plan of Action (JCPOA) – China, Russia, Germany, France, the United Kingdom and the European Union – hold meetings.
The US and Iran delegations will be in separate rooms, with EU representatives shuttling between them.
The negotiations are aimed at getting all parties back on side after the US – under then-president Donald Trump – withdrew from the pact in 2018.
The deal was aimed at making it harder for Iran to develop a nuclear weapon.
And Tehran agreed to curb its nuclear programme in exchange for the lifting of economic sanctions.
So, what are the challenges ahead?
Hillary Mann Leverett – former US diplomat and co-author of Going to Tehran
Hamed Mousavi – professor of political science at University of Tehran
Tariq Rauf – former head of the Verification and Security Policy Coordination Office at the International Atomic Energy Agency