Iran and world powers have failed to clinch a deal on Tehran's disputed nuclear programme despite intensive negotiations but will meet again on November 20 for fresh talks, officials say.
EU diplomatic chief Catherine Ashton said late on Saturday that there had been "three days of intense and constructive discussions" but that Tehran and the P5+1 group of world powers, consisting of the US, UK, France, China, Russia, Germany and the EU, would have to meet again.
"A lot of concrete progress has been achieved but some issues remain," she said, adding: "Our objective is to reach a conclusion and that's what we'll come back to try to do."
Iranian Foreign Minister Mohammad Javad Zarif said he was not discouraged despite the failure of the talks.
"I'm not disappointed at all because the meeting we just had, very long, running after midnight, was a good meeting," Zarif said. "We are working together and hopefully we will be able to reach an agreement when we meet again."
The meeting went late into the night on Saturday, reported Al Jazeera's James Bays in Geneva, where the talks were being held.
"There is certainly frustration but there is no doubt progress has been made here," he said. "After a decade of wrangling, just getting this far is an achievement."
The main sticking points appeared to include calls for shutdown of the Arak nuclear reactor southeast of Tehran that could eventually help produce weapons-grade nuclear fuel, the fate of Iran's stockpile of higher-enriched uranium and the nature and sequencing of relief from economic sanctions sought by Tehran.
Prospects for an agreement dimmed after French Foreign Minister Laurent Fabius raised objections to a draft that the French had previously agreed to.
Fabius spoke of "several points that ... we're not satisfied with compared to the initial text," telling France-Inter Radio his nation does not want to be part of a "con game".
Although Kerry publicly played down the differences with Fabius, other diplomats at the talks said the last-minute objections came as a surprise and complicated the chances of agreement.
Addressing the press following the meeting, US Secretary of State John Kerry said that Washington remains "determined to make certain" Iran does not acquire a nuclear weapon. While Kerry expressed optimism that a deal would be struck in the coming weeks, he also said that the window for a diplomatic solution would not be open "indefinitely".
The meeting on November 20 will occur at the political directors level, but Kerry suggested that foreign ministers could reconvene shortly after that date.
The Western powers remain concerned that Iran is continuing to amass enriched uranium not for future nuclear power stations, as Tehran says, but as potential fuel for nuclear warheads.
They are searching for a preliminary agreement that would restrain Iran's nuclear programme and make it more transparent for UN anti-proliferation inspectors.