U.S. Secretary of State John Kerry says an Iranian nuclear agreement is possible this week if Iran makes the "hard choices" necessary, but stresses "we are not yet where we need to be" on the most difficult issues.  Kerry and Iranian Foreign Minister Mohammad Javad Zarif are trying to meet a Tuesday deadline for a final nuclear deal.  "Over the past few days we have, in fact, made genuine progress," Kerry told reporters Sunday in Vienna, adding the two sides "have never been closer" to a deal.  "At this point, the negotiation could go either way," he said, putting the onus on the Iranians to make tough decisions quickly. "Right now, we are aiming to try to finish this in the time frame that we've set out, that's our goal and we're going to put every bit of pressure possible on it to try to do so." Kerry is holding firm on the stance that the Americans are willing to walk away from the talks if they don't get willingness from the Iranians to move on issues that are important to the U.S.  "We want a good agreement, only a good agreement, and we are not going to shave anywhere at the margins in order just to get an agreement," he said, acknowledging "the world will analyse" the deal if an agreement is reached.  Foreign ministers from Britain, China, France, Germany and Russia were expected to begin arriving in Austria on Sunday evening as the major powers make a strong push to meet the deadline for a final agreement to end the 12-year-old dispute.  French Foreign Minister Laurent Fabius said on Sunday that the time was now up to Iran to decide whether it would make commitments on unresolved issues in nuclear talks with major powers.  "We are 72 hours from the moment when (these negotiations) are supposed to end," he said.  "The principle question is to see whether Iran will accept to make clear commitments on what has not been clarified. We hope so," he said. "Everything still has to be clarified and France's attitude will be the same as always — constructive firmness."
While both the U.S. and Iran acknowledge they've never been closer to an agreement, there are still critical issues that need to be ironed out ahead of Tuesday's deadline.