Top Western diplomats converged on the Austrian capital Friday to try to negotiate a nuclear deal with Iran before the deadline Monday, but they appeared to remain far apart as the day ended.
Secretary of State John F. Kerry met in Vienna with Iranian Foreign Minister Mohammad Javad Zarif, British Foreign Secretary Philip Hammond, French Foreign Minister Laurent Fabius and European Union envoy Catherine Ashton in a round robin of meetings at the stately Palais Coburg hotel.
The day's dramatic high point came when Iranian officials said Zarif would return to Tehran to present leaders there with the latest proposal from the six world powers that have been seeking a deal.
The trip seemed to set the stage for a conclusion to the year's search for a nuclear agreement. But it was abruptly canceled in midafternoon, and Iranian officials said Zarif would probably stay through the weekend to continue grinding away at the disputed issues.
Iran's Foreign Ministry said later that the world powers – Britain, China, France, Germany, Russia and the United States -- hadn't laid down any new proposal that required a top-level review.
Hammond, who flew in for four hours before returning to London, acknowledged that a "very significant gap" remained between the parties.
The two sides are seeking a deal that would lift harsh international sanctions on Iran if it accepts restrictions designed to assure that it does not use its expanding nuclear program to gain bomb-making capability.
Many officials and outside experts expect the seven countries won't be able to reach a deal by midnight Monday and will instead extend the negotiations.
Yet there remains a chance that the sides are holding out until the last minute for compromises in hope of getting the best possible terms. One year ago, Iran and the six countries didn't reach an agreement on a temporary nuclear deal with Iran until hours after a midnight deadline.
The stakes are high. Senior Obama administration officials say a further delay would greatly reduce the chances of a deal, which is President Obama's highest foreign policy priority.
Kerry remained in Vienna later than planned Friday evening to continue talks, though he was expected to fly later to Paris for more consultations over the weekend, before returning to Vienna by Monday. Other foreign ministers were expected to return by Monday's deadline.
Kerry has insisted that the six nations had not discussed seeking an extension of the talks.
"We are driving toward what we believe is the outline of an agreement that we think we can have," Kerry said.
In Washington, meanwhile, lawmakers continued to call for the administration to insist on tough terms in any deal.
Eleven Republican senators-elect issued a statement Friday calling on Obama to make sure that any deal "effectively eliminates" Iran's nuclear program. The administration's proposals would allow Iran to continue its program as long as it is peaceful.
Forty-three Republican senators, including longtime sanctions advocate Sen. Mark Kirk of Illinois, have been pressing the administration to insist on a rollback, rather than simply a freeze, of the program.
Some Senate Democrats, including Sen. Charles E. Schumer of New York, Sen. Mark R. Warner of Virginia and Sen. Chris Coons of Delaware have also said in recent days that the administration should insist on tough terms in any deal.