Crunch talks between Iran and world powers stretched into an unscheduled third day on Saturday as top diplomats pushed for a deal to end the decade-old standoff over Iran's nuclear programme.
The US, British, French and German foreign ministers rushed to Geneva on Friday hoping to seal a breakthrough.
The hoped-for agreement -- seen as a first step ahead of further talks on a final deal -- could see Tehran freeze its nuclear efforts for as long as six months in exchange for some relief from the sanctions that have battered its economy.
Western officials, including US Secretary of State John Kerry, have expressed caution at the talks, warning major obstacles remain to be overcome.
Kerry, who cut short a Middle East tour to join the talks, said on arriving in Geneva: "There are still some very important issues on the table that are unresolved."
French foreign minister Laurent Fabius said early on Saturday that there were "some points on which we are not satisfied".
"There is an initial draft that we do not accept... I have no certainty that we can finish up" at this stage, Fabius told France Inter radio.
In a series of meetings early on Saturday, both Kerry and Fabius met with EU diplomatic chief Catherine Ashton, who has represented the six world powers at the talks.
The three were then to huddle together with British foreign secretary William Hague and his German counterpart Guido Westerwelle.
Talks between Kerry, Ashton and Iranian foreign minister Mohammad Javad Zarif continued until nearly midnight on Friday and were set to resume early Saturday.
Fabius was also to hold separate talks Saturday with Ashton and Zarif.