Iran's president Hassan Rouhani said on Sunday that its "rights to enrichment" of uranium were "red lines" that would not be crossed and that the Islamic Republic had acted rationally and tactfully during nuclear negotiations, Iranian media reported.

"We have said to the negotiating sides that we will not answer to any threat, sanction, humiliation or discrimination. The Islamic Republic has not and will not bow its head to threats from any authority," he said during a speech at the National Assembly, Iran's student news agency (ISNA) said.

"For us there are red lines that cannot be crossed. National interests are our red lines that include our rights under the framework of international regulations and [uranium] enrichment in Iran."

On Saturday, Iran and six world powers failed in talks to clinch a deal to curb Tehran's nuclear program but said differences had narrowed and they would resume negotiations in 10 days to try to end the decade-old standoff.

The talks ran into trouble Saturday after France raised objections to a draft agreement, complaining it did not go far enough to contain Iran's nuclear ambitions.

France's insistence on tough terms on Iran dispelled an atmosphere of optimism that had prevailed since the talks began Thursday. French Foreign Minister Laurent Fabius spoke of "several points that … we're not satisfied with compared to the initial text," telling France-Inter Radio his nation does not want to be part of a "con game."

Earlier, Iranian state TV strongly criticized the French position, calling France "Israel's representatives at the talks," while Iran's IRNA news agency cited Iranian President Hassan Rouhani as urging world powers to reach a deal.

U.S. Secretary of State John Kerry and foreign ministers of six other delegations conferred with Iranian Foreign Minister Mohammad Javad Zarif in a late-night session which broke up after midnight with no deal in place. 

Comments by Zarif increased skepticism that the two sides would agree on the full contours of a first-step deal at the current negotiating round.

"There are differences," Zarif told Iranian state TV, adding that if open questions remained after Saturday, the talks would reconvene within a week to 10 days.

Iran's Arak reactor southeast of Tehran could produce enough plutonium for several nuclear weapons a year once it goes online. Beyond differences over that part of Iran's nuclear program, Fabius said there was disagreement over efforts to limit Iran's uranium enrichment to levels that would require substantial further enriching before they could be used as the fissile core of a nuclear weapon.

French Foreign Ministry spokesman Romain Nadal said the powers negotiating with Iran were broadly united and that France wanted "the international community to see a serious change in the climate" of talks with Iran.

"There have been years of talks that have led to nothing," Nadal said, alluding to the need for tough terms on Iran.

Iran insists it is pursuing only nuclear energy, medical treatments and research, but the U.S. and its allies fear that Iran could turn this material into the fissile core of nuclear warheads. Iran currently runs more than 10,000 centrifuges that have created tons of fuel-grade material that can be further enriched to arm nuclear warheads.

It also has nearly 200 kilograms of higher-enriched uranium in a form that can be turned into weapons much more quickly. Experts say 250 kilograms of that 20 per cent-enriched uranium are needed to produce a single warhead.

Reactor ready next year 

Iran says it expects Arak, the plutonium producing reactor, to be completed and go online sometime next year. It would need additional facilities to reprocess the plutonium into weapons-grade material, and the UN's nuclear agency monitoring Iran's atomic activities says it has seen no evidence of such a project.

Fabius said Iran opposes suspending work on Arak while nuclear negotiations go on. He said France considers suspension absolutely necessary.

Iran also is being asked to blend down "a great part of this stock at 20 per cent, to 5 per cent," Fabius said. Uranium enriched to 5 per cent is considered reactor fuel grade, and upgrading it to weapons-level takes much longer than for 20 per cent enriched uranium.

Fabius suggested that the six powers were looking for an Iranian commitment to cap future enrichment at 5 per cent.

Kerry arrived in Geneva on Friday followed by counterparts from Russia, China, Britain, France and Germany with the talks at a critical stage following a full day of negotiations Thursday. He said some obstacles remained in the way of any agreement offering sanctions reductions for nuclear concessions.

Catherine Ashton, the European Union's foreign policy chief, is overseeing the talks.

With files from Reuters