Iran's chief negotiator has urged western governments to finalise a deal at the Vienna talks on rescuing the 2015 agreement limiting Iran's nuclear programme in exchange for the lifting of sanctions.
"No matter how close we are to the finish line, there is not necessarily a guarantee to cross it," Ali Bagheri tweeted from Tehran, where he had flown on Wednesday for consultations as Tehran announced that the negotiations are in a "critical stage". He is due to return to the talks on Friday.
Mr Bagheri was replaced in Vienna by his deputy and head of Iran's Atomic Energy Organisation Behrouz Kamalvandi, who arrived for "technical consultations" with the International Atomic Energy Agency, which monitors Iran's nuclear programme.
Despite western leaders' focus on Russia's invasion of Ukraine, the negotiations appear to be progressing towards a climax.
Iran's foreign minister Hossein Amir-Abdollahian said the talks have reached "a critical and important stage" and expressed hope that unresolved issues will be addressed by the western side – the remaining European signatories Britain, France and Germany, and the US, which pulled out of the deal in 2018 and imposed sanctions.
Russia and China have not, reportedly, been side-tracked by the Ukraine crisis, and continue to play a positive role.
The Ukraine conflict could inject momentum into the Vienna talks as western governments have come under pressure to find alternative sources to Russian natural gas and oil exports on which Europe depends. The price of gas could double and the price of oil has already soared to $100 a barrel for the first time since 2014.
Once sanctions curbing Tehran’s exports are lifted, Iran could make up for a portion of disruptions of supplies to Europe.
At this week's gas summit held in Qatar, Iran's oil minister Javad Owji said: "Iran has repeatedly announced that it enjoys necessary capacity to supply gas to neighbouring countries and even Europe."
Iran has vast untapped gas reserves, is currently producing 2.5 million barrels of oil a day and can quickly increase this by 1 million. Iran also has quantities of crude stored on vessels ready for delivery.
In Vienna, the Iranians have, reportedly, dropped their demand for guarantees that the US will not abort the deal a second time if there is a change of administration.
Iran continues, however, to insist that the US cancellation of sanctions is verified and an end to measures on key Iranian figures, including supreme guide Ayatollah Ali Khamenei, and Iranian Revolutionary Guards.
Iran has also proposed a prisoner swap as a confidence-building measure in exchange for the US release of $7-8 billion in blocked Iranian accounts in foreign banks.
US chief negotiator Robert Malley has stated repeatedly that there can be no deal without the return home of four dual US-Iranian citizens imprisoned in Iran.