High-level negotiations on Iran’s nuclear programme enter their last day on Tuesday before a deadline for agreeing the outline for a comprehensive settlement, with top diplomats still struggling to overcome persistent obstacles.

The US secretary of state, John Kerry, his Iranian opposite number, Mohammad Javad Zarif, alongside foreign ministers from France, the UK, Germany and China, worked late into the evening on two consecutive nights in an effort to break the deadlock.

Russia’s Sergei Lavrov left the talks on Monday afternoon to hold official meetings in Moscow, but said he would return to Lausanne later on Tuesday, telling reporters in the Russian capital that there was a good chance of success.

“The chances are high. They are probably not 100% but you can never be 100% certain of anything. The odds are quite ‘doable’ if none of the parties raise the stakes at the last minute,” Lavrov said on Tuesday.

A US State Department spokeswoman said on Monday night that prospects of a deal on Tuesday were “50-50”. Working teams of experts and diplomats were instructed to work through the night on outstanding issues in the search for a breakthrough.



Diplomats said that the principal sticking point was the issue of UN security council sanctions on Iran. Zarif’s team is sticking by the demand by their country’s supreme leader, Ali Khamenei, for all sanctions to be lifted at once in return for Iranian acceptance of restrictions on its nuclear programme over a period of at least 10 years.



The six-nation group is offering several relief measures, lifting the EU oil embargo and removing banking restrictions in moves synchronised with the suspension of corresponding US sanctions. But it insists that some UN sanctions must stay in place until Iran has convinced the international community it has no intention of pursuing a weapons programme, a task that could take many years.

European diplomats said the final day of talks would show whether Iran’s seemingly immovable stance on UN sanctions was a hardball negotiating tactic, or whether Khamenei had left them no negotiating space. Khamenei said on his website on Monday morning: “Sanctions must be lifted in one go, not as a result of future Iranian actions.”

Iran’s nuclear negotiations: how did we get here? – video explainer Guardian

In a further sign of problems at the talks, Khamenei’s foreign policy adviser, Ali Akbar Velayati, cast doubt on the west’s motives at the talks.



“Our negotiating team are trustworthy and compassionate officials that are working hard, but they should be careful with the enemies’ deceptive and skilful tactics,” Velayati told Fars news agency.

A diplomat in Lausanne quoted by the Chinese news agency Xinhua said the atmosphere on Monday had turned from optimism to gloom among negotiators.

Another longstanding hurdle to an agreement, the question of Iranian research and development, has been partially resolved. Iran has accepted strict limits on its development of new super-efficient centrifuges during the first 10 years of a deal, but there are disagreements on what would happen afterwards.



The six-nation group wants restrictions to extend for a further five years, wary that new centrifuges could drastically reduce Iran’s breakout time (the period it would need to build a bomb, should it make that decision). Iran rejects such prolonged curbs on its centrifuge development, saying it would render the country dependent on foreign technology.

A third problem seems to have been largely resolved in the past few days. Iran wanted to keep some centrifuges spinning at its underground enrichment plant in Fordow. The six powers negotiating with Tehran proposed a compromise in which a few hundred centrifuges spin but do not process uranium. They would purify other elements used for medical and scientific purposes.

Reza Marashi, research director of the National Iranian American Council, said even if the 31 March deadline was missed, none of the parties at the table would walk away.

“Both sides stand to lose massively. There is a propensity to focus on minutiae, but what has got lost is how much each side has to lose,” Marashi said. “Are we going to let this collapse over differences on how long Iran isn’t allowed to work on new centrifuges?”