Iranian officials said talks with world powers on the country's nuclear programme had reached a "critical" stage, as US Secretary of State John Kerry and his European counterparts held negotiations with Iran's top diplomats late into the night.
Talks were set to resume in Geneva on Saturday, with France cautioning that there was no certainty they would succeed because of major stumbling blocks over an initial proposed text on a deal..
The night before, talks between the Iranian delegation, led by Foreign Minister Javed Zarif, US Secretary of State John Kerry and EU Foreign Affairs chief Catherine Ashton, ended with all sides hailing the progress that was made throughout Friday's negotiations.
"We are reaching a very critical important point,'' Iranian Deputy Foreign Minister Abbas Araqchi said in comments broadcast on Iranian PressTV before the meeting.
"The negotiations have reached its critical, very sensitive situation, and it needs decisions at higher levels," he said, a reference to the arrival of the foreign ministers.
Before meeting Zarif on Friday night, Kerry said that significant differences between Iran and six world powers trying to fashion the nuclear agreement remained, as he and three European foreign ministers added their weight to try to narrow the gap.
We hope to try to narrow these differences but I don't think anybody should mistake there are some important gaps that have to be closed
"I want to emphasise there is not an agreement at this point," Kerry said shortly after arriving in Geneva, tempering rising anticipation of a breakthrough.
"We hope to try to narrow these differences but I don't think anybody should mistake there are some important gaps that have to be closed," he told reporters.
Kerry met his European counterparts before joint talks with Zarif, and Ashton, the EU's top diplomat, who has convened the talks.
Al Jazeera’s James Bays, reporting from Geneva, said: "There are also reports that the Chinese foreign minister will be here. It will mean the whole of P5+1, all will be represented at foreign minister-level. It shows they believe that possibly, with a nudge, they can get some sort of a historic deal."
France's foreign minister said that major questions still remained to be answered during the talks.
"France wants a credible accord on Iran's nuclear programme," Laurent Fabius said in a statement sent to Reuters.
Meanwhile, Iran has told Western powers that it wanted them to consider easing oil and banking sanctions during the first phase of any interim nuclear deal they agree to, an Iranian delegate at the talks said on Friday.
"We have announced to the West that in the first phase the issue of banking and oil sanctions must be considered," Majid Takht-Ravanchi, a member of Iran's negotiating team in Geneva, was quoted as saying by Iran's Mehr news agency.
Rollback of sanctions
The talks primarily focus on the size and output of Iran's enrichment programme, which can create both reactor fuel and weapons-grade material suitable for a nuclear bomb.
Iran insists it is pursuing only nuclear energy, medical treatments and research, but the United States and its allies fear that Iran could turn this material into the fissile core of nuclear warheads.
Six powers - the negotiators also include Russia and China – are considering a gradual rollback of sanctions that have crippled Iran's economy.
In exchange they demand initial curbs on Iran's nuclear programme, including a cap on enrichment to a level that can be turned quickly to weapons use.
But their proposal would maintain core sanctions on Iran's oil exports and financial sector, as an incentive for Iran to work toward a comprehensive and permanent nuclear accord.
Russian Foreign Minister Sergey Lavrov, who spoke of "a chance for reaching agreement on a common approach" despite the remaining differences, is heading to Geneva to attend the talks.