VIENNA – Iran and six world powers are closer than ever to a deal that would crimp Tehran's ability to make nuclear arms — a status that would lead to an end to sanctions on the Islamic republic and ease tensions that could boil over into a new Middle East war.
The bad news? Substantial differences remain. A deal by the Nov. 24 target date is unlikely. Both sides may be willing to extend. But that could strengthen opposition in U.S. Congress, triggering a backlash by Iranian hardliners and culminating in the breakup of further negotiations.
With so much at stake, U.S. Secretary of State John Kerry and his counterparts from Russia, China, Britain, France and Germany are planning to join Iranian Foreign Minister Mohammad Javad Zarif at the Vienna talks after they resume Tuesday.
A look at where things stand — and where they may go.
WHAT DO BOTH SIDES WANT?
The six powers want to dent Iran's ability to make nuclear arms. Experts say Tehran now could do that within three months. The U.S. and its allies want that timeline extended to give them time to react.
"The American objective is to push (nuclear weapons') breakout time to a year or more," says Gary Samore, who was part of the U.S. negotiating team with Iran until last year.
Tehran says it doesn't want nuclear arms and is interested only in peaceful atomic programs, including making reactor fuel. It seeks not only to keep its present program, but to greatly expand it in the near future. At the same time, it is seeking an end to nuclear-related international sanctions imposed over its refusal to curb its nuclear activities.
WHAT IS THE MAIN DISPUTE?
Iran's uranium enrichment program. Enrichment can produce reactor fuel or the fissile core of a warhead. The U.S. and its allies want deep, lasting cuts in the program — something Tehran has refused to accept up to now.
HAS THERE BEEN PROGRESS?
Yes. The U.S. originally demanded that Iran cut the output of its enrichment program to the equivalent of what 1,500 of its mainstay centrifuges — the machines that enrich uranium — produce. Diplomats tell The Associated Press that going into Tuesday's talks, Washington is now ready to accept output equivalent to 4,500 such machines. But Iran must make other concessions in return.
One would be a reduction in Iran's stockpile of uranium gas, which is fed into the centrifuges at the start of the enrichment process. Like a cut in centrifuge numbers, this would accomplish the goal of reducing the time it would take Iran to enrich enough uranium for one bomb.
Iran was originally cool to the idea. But diplomats say it is now discussing it with Russia, which would store any excess stockpile. Samore, who is now with Harvard's Belfer Center for Science and International Affairs, says Washington "would accept any solution" that reduces Iran's breakout time to at least a year.
CHANCES OF A NOV. 24 DEAL?
Unlikely. Iran originally said it wants to keep its roughly 10,000 centrifuges running. Diplomats tell the AP it now could accept 8,000. But that is still substantially above U.S. demands, regardless of how much its uranium gas feedstock is reduced.
And Tehran continues to insist that enrichment constraints end after only a few years. After that, it wants to produce enriched uranium equal to the output of nearly 200,000 of its present-day centrifuges. Washington demands an enrichment clampdown of more than a decade.
Differences also remain over the future use for a bomb-resistant Iranian underground enrichment site and over a nearly completed nuclear reactor that would produce enough plutonium for several bombs a year if finished according to present specifications. But diplomats say those can be eliminated quickly, if there is agreement on enrichment.
WHAT HAPPENS IF THE DEADLINE IS MISSED?
Both sides will likely opt for extending talks to stave off a spike in tensions that could ultimately lead to military confrontation. But missing the Nov. 24 deadline will feed skepticism in U.S. Congress.
The U.S. administration might try to appease Congress by considering new sanctions "triggered" by a lack of progress in new negotiations. But that could strengthen Iranian hardliners and result in Tehran walking away from the negotiating table.