Six world powers and Iran launched a decisive chapter in diplomacy on Wednesday to begin drafting a lasting accord that could curb Tehran's contested nuclear program in exchange for a phased end to sanctions that have hobbled the Iranian economy.
This latest negotiating round, which includes the U.S., Russia, China, France, Britain and Germany, in addition to Iran, comes a little more than two months before a July 20 target date for an agreement.
The six world powers hope to reduce Iran's potential nuclear-weapons-making capacity by negotiating substantial cuts in its atomic program. Tehran says it does not want such arms and is ready for concessions in exchange for an end to all sanctions on its economy.
A spokesman for European Union foreign policy chief Catherine Ashton, who coordinates diplomacy with Iran on behalf of the six countries, said negotiators held a "useful initial discussion" on Wednesday morning and would hold coordination meetings later in the day.
"We are now hoping to move to a new phase of negotiations in which we will start pulling together what the outline of an agreement could be. All sides are highly committed," the spokesman said.
Despite some progress over months of talks, diplomats say substantial differences remain and an accord in two months is far from assured, with Western diplomats warning that divisions could prove insurmountable.
"Quite frankly, this is very, very difficult," a senior U.S. official told reporters on the eve of the talks, speaking on condition of anonymity. "I would caution people that just because we will be drafting it certainly does not mean an agreement is imminent or that we are certain to eventually get to a resolution."
Tehran has about 10,000 nuclear centrifuges running, but the West will likely want that number trimmed to the low thousands, a demand that could be unacceptable to the Islamic Republic.
Iran's research and development of new nuclear technologies and the amount of stockpiled enriched uranium it may keep will also be crucial and likely difficult to negotiate. Refined uranium can be used as fuel in nuclear power plants or in weapons if purified to a high enough level.
"Halting research and development of uranium enrichment has never been up for negotiation, and we would not have accepted it either," Iranian Deputy Foreign Minister Abbas Araqchi was quoted as saying by the ISNA news agency. "But a wide variety of issues have been discussed ... and on uranium enrichment too we have tried to reach consensus."
Iran entered talks with the big powers after moderate President Hassan Rouhani was elected last June. The talks follow a first-step deal in which Tehran agreed in November to temporarily stop expanding its nuclear activities in return for some sanctions relief.
Looming in the background of the talks have been threats by Israel — widely believed to have the Middle East's only nuclear weaponry but which sees Iran as an existential threat — to attack Iranian nuclear installations if it deems diplomacy ultimately futile in containing Tehran's atomic abilities and potential. U.S. President Barack Obama has not ruled out the last-ditch option of military action either.
Divisions in Washington are closely linked to concerns in Israel that any deal might not go far enough.
"We are not against diplomatic solutions," Yuval Steinitz, Israel's minister in charge of nuclear affairs, told reporters in Brussels last week. "But on the one condition that it is a serious and comprehensive solution. A solution that can be trusted."