Barring a late breakthrough, talks between Iran and six world powers on Tehran's nuclear programme are likely to end without an agreement.

They are expected to resume in a few weeks, Western diplomats said.

Earlier, France said there was no certainty nuclear talks under way with Iran in Geneva would succeed because of major stumbling blocks over an initial proposed text on a deal.

Top diplomats from Iran and six world powers are in a third day of negotiations over Iran's nuclear programme to try to end a decade-old standoff.

The West suspects that Iran is enriching uranium to develop nuclear weapons capability. Tehran denies this.

"As I speak to you, I cannot say there is any certainty that we can conclude" the talks, French Foreign Minister Laurent Fabius said on France Inter radio, noting that France could not accept a "sucker's deal".

Among the sticking points for Paris, Mr Fabius said that France wanted Iran to stop operations at its Arak reactor during the negotiations and said there were questions about Iran's stock of uranium enriched to 20%.

France has traditionally taken a tougher line on Iran than most other world powers and Iranian Foreign Minister Mohammad Javad Zarif has accused it of being more intransigent in talks than the United States.

The talks have deeply upset some of Iran's traditional enemies in the region such as Israel, whose Prime Minister Benjamin Netanyahu said the Jewish state "utterly rejects" a deal.

"The security concerns of Israel and all the countries of the region have to be taken into account." Mr Fabius said.

"We are for an agreement, that's clear. But the agreement has got to be serious and credible. The initial text made progress but not enough," he said.

The negotiations, originally planned as a two-day meeting to end yesterday, are expected to finish later today.