The landmark international nuclear agreement with Iran comes into force Sunday with some key questions about implementation still unanswered.
The U.S. and five other world powers will begin taking steps that, over the next half a year or so, will remove economic sanctions on Iran as it rolls back nuclear activities to prevent it from obtaining a nuclear bomb.
Both the Iranian and U.S. governments appear strongly committed to following through on the deal, reached July 14 in Vienna after a dozen years of negotiations.
Yet they still haven't sorted out all the tricky questions on how Iran's nuclear program will be monitored, how fully sanctions will be eased, and how harshly violations of the rules will be dealt with by world powers, among other issues.
Disagreements on these could lead to continuing battles and delays in implementation, though they're not expected to sink the agreement, diplomats and outside experts say.
"There are potentially contentious issues in there," said Gary Samore, a former arms control advisor to President Obama who is now executive director for research at the Harvard Kennedy School's Belfer Center for Science and International Affairs.
The two sides may disagree over:
Monitoring. Iran and the United Nation's nuclear watchdog agency, the International Atomic Energy Agency, have yet to sort out all details of how inspectors will keep an eye on nuclear activities, such as uranium enrichment. The agreement is specific on many points, but some important details can be settled only as the new restrictions are put in place, experts say.
The nuclear agency is likely to push for strict oversight, and Iran may object to some steps as infringement of its sovereignty.
Iran is expected to provide a complete inventory of its key nuclear hardware; the world powers may react strongly if they believe Iran is hiding something.
Sanctions. The United States and the European Union are committed to lifting punishing sanctions on trade, investment and energy after Iran takes steps such as storing its centrifuges and redesigning a heavy-water nuclear reactor. But how much sanctions relief is in store remains uncertain.
The United States and the European Union are going to maintain sanctions that were imposed on Iran for human rights and terrorism infractions. It's not entirely clear how closely they will enforce the rules, experts say. And they may add more sanctions if, for instance, they see Iran using armed proxies aggressively in its region.
The two sides are already at odds over sanctions that the agreement continues on Iran's trade in conventional arms and ballistic missiles systems. Iran is insisting that it will not heed those rules, and last weekend fired an intercontinental ballistic missile to test its technology. The Obama administration said the test was a sanctions violation because the missile was capable of carrying a nuclear weapon, and appealed to the United Nations to enforce the rules.
President Obama, at a press conference Friday, stopped short of threatening Iran with new U.S. sanctions over the missile test, but said U.S. officials would try to "build pressure on them" to convince them to halt "bad behavior."
With this uncertainty, many major international businesses are hanging back from doing business in Iran, for fear they will run afoul of U.S. and European regulators, with potential damage to their reputations.
"Who is going to go into Iran, and how much, is still very much up in the air," said Adam M. Smith, a former U.S. sanctions official who is now of counsel at the Gibson, Dunn & Crutcher law firm.
Penalties. The world powers and Iran haven't yet worked out how tough the penalties will be for various infractions of the agreement. That will be sorted out over time, as allegations of violations are sent to a body called the Joint Commission, consisting of Iran, the six world powers and the European Union.
Some U.S. allies, such as Israel, are worried that the six powers will be too reluctant to impose tough penalties because it could risk sinking the agreement. But Richard Nephew, a former member of the U.S negotiating team now at Columbia University, says that for deterrence reasons, it is preferable for the government not to precisely spell out what penalties they'll impose.
"Ambiguity has some deterrence value," he said.