Talks between Iran and six Western powers on curbing Iran's nuclear ambitions ended on Saturday without an agreement.
EU foreign policy commissioner Catherine Ashton said the talks would continue on 20 November.
Diplomats in Geneva said a split had emerged between France and the other nations. France wants tougher terms for Iran.
Foreign Minister Laurent Fabius said Paris could not accept a "sucker's deal".
"As I speak to you, I cannot say there is any certainty that we can conclude," he told France Inter radio.
Mr Fabius earlier said Iran was resisting French demands that work on a plutonium-producing reactor be suspended and its stockpile of higher-enriched uranium be downgraded.
Another sticking point mentioned by Mr Fabius was that Tehran was resisting demands to downgrade its stockpile of uranium enriched to 20%.
Iranian Foreign Minister Mohammad Javad Zarif told the BBC he was more cautious about a deal than two days ago, but was hopeful an agreement would still come.
US Secretary of State John Kerry unexpectedly arrived on Friday from the Middle East to join the talks on a plan to freeze parts of Iran's atomic programme in exchange for sanctions relief.
Although details of the suggested accord have not been disclosed, the BBC says it is thought to offer Iran a gradual easing of sanctions in return for a freeze on expansion of nuclear activities.
While an agreement this weekend appears unlikely, Western diplomats say the talks are expected to resume within a few weeks.
Foreign ministers from Britain, France, Germany, Russia and the United States took part in Saturday's talks. China sent a deputy foreign minister, who arrived on Saturday evening.
A member of Iran's negotiating team, Majid Takt-Ravanchi, told the Mehr news agency on Friday that Western powers should consider easing oil and banking sanctions during the first phase of any deal.
Since 2006 the UN Security Council has imposed a series of sanctions on entities and people involved in Iran's nuclear programme.
Separate US and EU sanctions have targeted Iran's energy and banking sectors, crippling its economy.
