WASHINGTON (AP) — U.S.-Iranian nuclear talks are the biggest source of tension in the relationship between President Barack Obama and Israeli Prime Minister Benjamin Netanyahu.

The American leader is pushing for a framework deal with Tehran by the end of March and a full accord by July. Netanyahu opposes any deal that leaves the Iranian nuclear program intact.

Negotiators from the U.S., world powers and Iran have sought to keep the details of a potential agreement secret. But the statements of governments, anonymous officials and think tanks closely monitoring the discussions give some idea of what may be included in an agreement.

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URANIUM ENRICHMENT:

For all sides, Iran's enrichment of uranium is the top priority. The material can be used for peaceful energy generation, which Iran declares as its objective, or producing a nuclear warhead. An interim nuclear agreement with Iran in late 2013 capped the number of Iranian centrifuges enriching uranium at 9,000. The United States wants to bring that number down further. Officials have spoken of 6,500 as a possible agreement, if Iran only enriches with its basic centrifuge model and ships out much of its stockpile of already enriched material to Russia. For the U.S. and its partners, those elements together aim to ensure that the length of time Iran would need to surreptitiously "break out" toward a nuclear weapon is at least one year. The interim deal halted Iranian enrichment of material at levels approaching weapons grade. That constraint will continue. U.N. nuclear agency inspectors will monitor compliance.

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UNDERGROUND FACILITY:

Iran's once-secret, underground enrichment facility at Fordo poses a unique problem because of the difficulty any country would have in eliminating it militarily. The Israelis and hawks in the U.S. Congress hoped to see the site dismantled. A likelier compromise would have Iran restrict the bunker for research purposes, though details from the talks are hazy.

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PLUTONIUM:

Iran's heavy water reactor at Arak presents a potential, alternative route to a bomb because it could produce enough plutonium for a couple of nuclear weapons each year. The plutonium path isn't as far along as the uranium path. Still, negotiators hope to neutralize the site as a future threat. Possible solutions include shutting the facility down or turning it into a light water reactor, which the U.S. and the West would prefer. Another option could be to reconfigure Arak so its plutonium output decreases significantly, perhaps as low as 5 percent of what the current design would produce.

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TIMESPAN:

How long the constraints last has been a source of tension. The U.S. had sought a 20-year deal; Iran wanted a timespan closer to 7 years. Officials have described the possibility of the full restrictions remaining in place for at least a decade. Then, Iran would be rewarded for good behavior by a gradual easing of conditions over the last five years of a deal. A shorter length could have regional repercussions with countries such as Saudi Arabia keeping a wary eye on the negotiations. Washington and its partners are adamant that heightened inspections won't be scaled back.

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SANCTIONS RELIEF:

The main carrot for Iran is the promise of less economic pressure. The Iranians want immediate relief; the U.S. and its partners are speaking of a phased approach. That would involve Obama suspending some restrictions immediately through executive action, and others over time. A final tranche could only come if the U.S. Congress acts to remove the sanctions permanently from American law. That seems unlikely in the short-term. Republicans and many Democrats in Congress are threatening new sanctions on Iran, supported by Netanyahu. Obama says such action risks scuttling the diplomacy and paving a path to war.

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OTHER MATTERS:

Iran's history of deception has many in Israel and elsewhere demanding it come clean with the International Atomic Energy Agency on any previous military aspects of its nuclear program. The IAEA has consistently said some of its questions remain unanswered. U.S. officials say the issue will have to be addressed in an agreement, yet haven't explained how. Iran's research and development activity is described as another of the trickiest matters still outstanding.