The envoys said a provisional agreement may be reached even earlier — by late last night. However, they warned that the final details of the pact were still being worked out and a formal agreement must still be reviewed by leaders in the capitals of Iran and the six world powers at the talks.
Senior US and Iranian officials suggested, however, that there was not enough time to reach a provisional deal by the end of yesterday.
“We are working hard, but a deal tonight is simply logistically impossible,” the Iranian official said, noting that the agreement will run to roughly 100 pages.
The senior US official declined to speculate as to the timing of any agreement or announcement, simply saying: “Major issues remain to be resolved.”
Despite the caution, the negotiators appeared to be on the cusp of an agreement.
US Secretary of State John Kerry, who on Thursday had threatened to walk away from the negotiations, said yesterday that “a few tough things” remain in the way but added “we’re getting to some real decisions”.
On route to Mass at Vienna’s gothic St Stephen’s Cathedral, Kerry said twice he was “hopeful” after a “very good meeting” on Saturday with Iranian foreign minister Mohammad Javad Zarif, who had Muslim services on Friday.
French foreign minister Laurent Fabius was also cautiously optimistic, telling reporters: “I hope that we are finally entering the last phase of this negotiation.”
In another sign that a deal could soon be sealed, Russian news agencies reported that Russian foreign minister Sergey Lavrov had arrived in Vienna. Chinese counterpart Wang Yi was expected later in the day.
Most other foreign ministers of the six nations negotiating with Iran are already in the Austrian capital and in position to join Kerry and Zarif for any announcement.
Movement toward a deal has been marked by years of tough negotiations. The pact is meant to impose long-term, verifiable limits on nuclear programmes that Tehran could modify to produce weapons. Iran, in return, would get tens of billions of dollars in sanctions relief.
The current round of talks is in its 16th day and has been extended three times since the first deadline of March 31 was missed. The mood among negotiators had turned sombre each time a new target date was set.
As the weekend approached, Kerry declared the talks couldn’t go on indefinitely and warned that the US could walk away from the negotiations.
Diplomats familiar with the talks said most of the nuts and bolts of implementing the deal have been agreed upon.