It has become a familiar diplomatic ritual going back a decade: western powers meet Iran hoping to curb its nuclear ambitions. When talks end in stalemate, Iran boosts its atomic programme, the West imposes tougher sanctions and the stakes become higher.
On Tuesday, after an eight-month hiatus, the ritual will resume in Kazakhstan, when Iran meets representatives from six world powers, including the United States.
Neither a breakthrough nor a breakdown is expected. Mutual mistrust runs deep, but there is also a mutual desire to avoid military conflict.
Many analysts believe the best that can be expected in Almaty, the former Kazakh capital, are steps towards an agreement on a preliminary confidence-building measure.
But more likely it will be "a sort of fudge" in which each side puts forward ideas for "exploration in further talks", said Sir Richard Dalton, a former British ambassador to Tehran and now an associate fellow at the Chatham House think tank.
Iran will be given an updated offer of sanctions relief in return for curbing key aspects of its nuclear programme, which the West suspects masks a drive to develop a weapon - a charge Tehran denies.
Western diplomats describe the offer as "substantial and serious" but have not divulged the details. Many experts, however, doubt it will improve much on the last offer that Iran rejected because it did not include a significant easing of sanctions.
Iran was asked to "give diamonds in exchange for peanuts", one former Iranian negotiator complained at the time.
The US is now reportedly ready to add a new inducement: lifting an embargo on Tehran's barter trade of oil for gold. Iran has already criticised the offer as insufficient because the precious-metals ban was introduced just weeks ago and so does not address earlier sanctions targeting its vital oil and banking sectors.
Even so, both sides have a vested interest in launching and sustaining what would be a long and laborious negotiating process that might make little headway before Iran's presidential elections in June, if at all.
Tehran has sent mixed signals in recent weeks, apparently to bolster its hand in talks with the six world powers. These comprise the UN Security Council's five permanent members - the US, Russia, China, Britain and France - plus Germany; the so called P5+1.
The UN's nuclear watchdog confirmed last week that Iran has begun installing - but not yet operating - a new generation of centrifuges at its main uranium enrichment plant in Natanz, drawing sharp rebukes from the West.
But the International Atomic Energy Agency (IAEA) also reported that Tehran has slowed down its accumulation of 20 per cent enriched uranium, which most concerns the West because that level of purity is within striking distance of making bomb-grade material.
So while Iran presses ahead on one nuclear front, it is being careful not to push the US and Israel too far on another.
Washington is also sending mixed messages. "The US offer of serious talks combined with escalating sanctions is as mixed as Iran's dual signals on its nuclear programme," said Farideh Farhi, an Iran expert at the University of Hawaii. "I would go even farther and suggest that Iran's mixed signals are a direct response to the dual track pursued by the US."
Tensions, however, have eased since the last round of talks between Iran and the P5+1 ended in stalemate in Moscow last summer. Israel has eased its sabre-rattling against Iran, while Washington's ability to strike a deal was increased by Barack Obama's re-election in November.
The US president has assembled what one Iran expert called "the most pro-Iran-engagement national security cabinet in recent US history". Congress, however, remains as rigidly anti-Iran as ever.
Iran, meanwhile, is preoccupied with an intensifying power struggle between its ruling conservative factions ahead of its own presidential elections.
"Partly because of these elections, Washington is hesitant to offer more at the moment because it knows Iran can't reciprocate until after the vote," said Trita Parsi, the author of A Single Roll of the Dice - Obama's Diplomacy with Iran.
"But also, there's the sense in Washington that sanctions are biting so hard in Iran that the US doesn't need to improve its offer," said Mr Parsi, who heads the Iranian National American Council, an advocacy group.
Previous negotiations were stymied by each side effectively calling on the other to make concessions up front before it delivers. Iran insists on "reciprocity", where concessions by one side are matched simultaneously by ones of equal value by the other.
The P5+1's immediate goal is for Iran to halt enriching uranium to 20 per cent. The six powers also want Iran to close its fortified underground bunker at Fordo where the enrichment takes place, and to send abroad its stockpile of the material.
Tehran insists it will not dismantle Fordo because it is impregnable to aerial attack by Israel and was built for that very reason. But Tehran repeatedly has signalled it could halt 20 per cent enrichment if the price is right.
That price is significant sanctions relief and formal recognition of Iran's "right" to enrich uranium up to 3.5 per cent, the level required to fuel electricity-generating reactors.
Maintaining a domestic nuclear fuel cycle is vital to Iran's leaders. They have invested national and personal prestige in a programme they champion as central to Iran's scientific prowess and independence.
Israel, the region's sole nuclear-armed power, has warned it could take military action against Iran's atomic facilities if the Islamic republic amasses 240 kilograms of 20 per cent enriched uranium, enough in theory to make one nuclear warhead if further purified. Israel had calculated that threshold would be reached by next summer.
But the IAEA reported last week that Iran in December resumed converting some of its 20 per cent enriched stockpile into fuel rods for a medical research reactor, rendering it all but useless for weapons purposes.
Iran now has 167 kg of 20 per cent enriched uranium, an increase of 32 kg in the past three months, according to the IAEA. At that rate, it would take Iran more than six months to reach Israel's "red line".
