Talks between the world's leading foreign ministers on Iran's nuclear programme are to stretch into an unscheduled third day after they ended on Friday with major "unresolved" issues remaining.
US Secretary of State John Kerry, who cut short a Middle East tour to attend the talks in Geneva, Switzerland, struck a note of caution after a five-hour meeting drew to a close last night.
"There is not an agreement at this point," Mr Kerry told reporters. "There are still some very important issues on the table that are unresolved."
A senior State Department official said: "Over the course of the evening, we continued to make progress as we worked to the narrow the gaps. There is more work to do."
Iranian deputy foreign minister Abbas Araqchi added: "It was productive but still we have lots of work to do."
Six world powers - the US, Russia, China, Britain, France and Germany - are working on a deal to cap some of Iran's atomic programme in exchange for limited relief from economic sanctions.
Russian foreign minister Sergei Lavrov said the six countries and Iran could agree a "road map" to end the differences over the programme at the talks.
Iranian foreign minister Mohammad Javad Zarif (centre) is at the talksMr Lavrov is expected to join the discussions today, diplomatic sources said.
He told reporters he did not wish to prejudge the outcome but said Iran should be allowed to have a peaceful nuclear programme under the watch of the International Atomic Energy Agency.
Unlike previous encounters between Iran and Western powers in the past decade, all sides have remained quiet about details of the negotiations, without the criticism and mutual allegations of a lack of seriousness that have been typical of such meetings in the past.
Diplomats involved in the talks say this is a sign of how serious all sides are.
If some sort of agreement is reached, it would be a breakthrough after a decade of negotiations between Iran and the six world powers.
A potential 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.
But Israel's prime minister Benjamin Netanyahu said on Friday that his country "utterly rejects" a deal being forged, adding that "Israel will do everything it needs to do to defend itself and defend the security of its people".