The official Iranian news agency IRNA said Kerry had made new proposals to the Iranians meant to bridge differences standing in the way of a deal.
A US statement earlier in the day said Kerry was heading for Paris and his "future travel schedule is still being finalized, and we have not yet determined when he will return to Vienna."
But he was still in Vienna, as the day turned into evening today. A new US statement said he had scheduled another meeting "tonight" with Iranian Foreign Minister Mohammad Javad Zarif and former EU foreign policy chief Catherine Ashton.
Iranian officials and media initially said Zarif was also departing today, heading to Tehran to consult after meeting with Kerry earlier in the day. But the official IRNA news agency later quoted an unidentified Iranian nuclear negotiator in Vienna as saying Zarif was staying "and the talks will continue."
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The US statement said Kerry would be consulting with European counterparts while in Paris. Diplomats said French Foreign Minister Laurent Fabius and British Foreign Secretary Philip Hammond left the Vienna talks in the afternoon after arriving earlier in the day.
Hammond held out hope for an agreement by Monday before meeting with Kerry and Fabius. At the same time, he told reporters that "we have a long way to go if we are to get to a deal before the deadline."
Both the Iranians and the six world powers negotiating with them must soon decide whether to go beyond Monday or adjourn to a later date. They may also opt to end negotiations, but that is unlikely.
Officials from the US, Russia, China, Britain, France and Germany are seeking to reduce the potency of Iran's nuclear program and slow its technical ability to produce atomic weapons. Iran denies seeking such arms, but is negotiating in pursuit of relief from international sanctions.