Iran nuclear deal hinges on enrichment limits, sanction relief

The current deadline to reach a comprehensive deal on the future of Iran's nuclear program is July 20. If no deal is reached by then, negotiators can decide to remain at the table for a further six months.

Given that, negotiators on both sides have today acknowledged that talks are "slow" and "difficult", a rollover looks very likely.

That is, unless the negotiations fail outright and we go back to a vicious cycle of the Iranians ramping up their nuclear program, and the West, led by the U.S., responding with even more draconian financial sanctions.

Even if the talks are extended for another six months, there are major obstacles in the way of a comprehensive agreement.

The main one for Western powers, says Mark Fitzpatrick from the London-based Institute of Strategic Studies, is the size and scope of the limits that Iran would have to accept on its enrichment program.

"Iran wants to keep all 20,000 of the centrifuges it now has installed; while the [U.S. and its allies at the table] insist that the number be cut to 4,000 or less."

For Iran, the major sticking point is sanctions relief.

President Obama's administration can offer to unblock tens of billions in frozen Iranian assets. However, the Iranians want more than that money. They want business links to the West, and access to the global banking system and financial markets.

Finally, the two sides fundamentally disagree on the length of time any comprehensive agreement would remain in effect. The P5+1 are talking about decades, while Iran wants all restrictions lifted after a few years.

Trita Parsi, president of the National Iranian American Council, says a long-term deal is unlikely.

"Iran will likely reject a deal that lasts beyond 10 to 15 years, not just because of the mistrust that exists between the two sides, but also because of the legitimate uncertainty that exists about the intentions and orientations of future leaders in Washington and Tehran." Parsi said.

In other words, Iran is willing to commit to limiting its nuclear program, but not for too long. In the negotiations, the West wants a comprehensive deal to be binding for decades. Iran wants all restrictions to end in just a few years.

So is there any cause for the kind of deft compromise that might yet produce a deal?

The astonishing lack of leaks from either side in the talks since January shows that the bargaining is serious, and relatively free of spin.

Also, there is already an agreement in principle on what everyone expected would be a major impasse: the plutonium-producing Arak heavy water reactor. The Iranians say they're willing to re-engineer it to minimize its plutonium output.

There is even a possible technical fudge on the issue of the number of centrifuges Iran is allowed to keep. It could reduce the number of operating machines, says Fitzpatrick, and keep the rest disassembled - for example, for spare parts.

In the end, the biggest problem is going to be the U.S. lifting sanctions.

Only the Congress can lift the sanctions that are embedded in law and the current political climate on Capitol Hill makes that extremely unlikely.