Talks on reviving the 2015 Iran nuclear deal are due to resume in Vienna today after they were suspended in June following the election of Iran's new hardline president Ebrahim Raisi.
The talks will be between Iran on the one hand and China, France, Germany, Russia, and the UK on the other.
The United States will also send a delegation, headed by US special envoy Rob Malley, which will participate in the negotiations indirectly.
President Biden is trying to salvage the deal, under which Iran agreed to limit its nuclear programme in return for relief from US, UN, and EU sanctions.
His predecessor, Donald Trump, withdrew from the agreement in 2018 and under a policy of maximum pressure imposed ever more punitive sanctions.
Iran, for its part, has raced forward with its nuclear programme, making it all but impossible to simply turn back the clock.
Speaking to Iranian state television on Sunday, Iran's top nuclear negotiator said the country's top priority would be to seek the removal of the crippling economic sanctions.
Ali Bagheri called the sanctions "illegal and oppressive" adding he hoped the "talks will effectively play a role in fulfilling Iran's goal of having these sanctions lifted".
But prospects of a breakthrough are slim.
Russia's ambassador to Vienna, Mikhail Ulyanov, also said that "informal meetings" between the participants would take place before the official start of the talks, which will be held at the Palais Coburg Hotel in the Austrian capital.
_Watch the full interview with Dr Sanam Vakil, deputy director of the Middle-East North Africa Programme at Chatham House, in the video player above. _