Negotiators arrived in Vienna on Tuesday for the last round of talks on reaching a comprehensive agreement on Iran's nuclear programme before next week's deadline.
Foreign ministers of the P5+1 group of world powers are expected to join the talks next week amid conflicting reports on the proximity of a deal.
The meetings this week were led by Iran's Foreign Minister, Mohammad Jawad Zarif, and the former European Union foreign policy chief, Catherine Ashton, who is continuing to lead the P5+1 team. However, the main push to reach an agreement from the Western side is coming from the American administration.
In addition to the State Department's lead negotiator, Under-Secretary of State Wendy Sherman, the Americans have sent to Vienna the retired senior diplomat William Burns, who was in charge of the back-channel through which the Obama administration negotiated with the Iranians last year.
Secretary of State John Kerry is expected to join the negotiations next week, along with other EU foreign ministers, in a last push to reach an agreement by the November 24 deadline.
The apparent American eagerness to reach an agreement has stoked fears in Jerusalem that President Barack Obama will authorise a "weak" agreement.
A consensus based on various leaks suggests that the contours of the deal are already clear. It is expected to revolve around a limit on the quantity of enriched uranium that Iran will be allowed to retain, while the majority of the material will be shipped to Russia for conversion to uranium rods which cannot easily be used to manufacture weapons-grade material.
At the same time, Iran has reportedly agreed to "re-design" its heavy-water reactor in Arak to produce less plutonium.
The main differences remaining between the sides are over the numbers of enrichment centrifuges that Iran will be allowed to continue operating, the speed at which sanctions will be removed and the period in which Iran will have to continue to submit to intense inspections by the International Atomic Energy Agency.
US and European diplomats have said that the differences are now bridgeable and Iranian officials have been equally positive in their public statements.
The Obama administration has assured Israel that any agreement will ensure that it will take Iran at least a year to build a nuclear weapon, should it decide to "break out" of the international inspection regime.
Prime Minister Benjamin Netanyahu, however, claims that the agreement being discussed will allow Iran to become a "nuclear threshold" state and has been lobbying vigorously against it.
The talks in Vienna are expected to last until at least the Monday deadline, and they are expected to continue for a few days longer. The interim agreement signed a year ago in Geneva was meant to be for only six months, but could be extended once again by extra months.
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