Iran and world powers failed to clinch a deal Sunday on Tehran's nuclear programme despite marathon talks in Geneva, dashing hopes of a long-sought agreement in the decade-old standoff.

But diplomats said significant progress had been made in three days of intense negotiations and that talks would resume here on November 20.

Hopes had soared after top world diplomats rushed to Geneva to join the talks, but faded after cracks began to show among world powers when France raised concerns.

Emerging in the early hours of Sunday from a last-ditch negotiating session, EU diplomatic chief Catherine Ashton and Iranian Foreign Minister Mohammad Javad Zarif said the two sides had not been able to come together on a deal.

"A lot of concrete progress has been achieved but some issues remain," Ashton said. "Our objective is to reach a conclusion and that's what we'll come back to try to do."

Zarif said he was not discouraged by the failure of the talks, saying the meetings had taken place in a positive atmosphere and that he hoped to reach an agreement at the next talks.

"I'm not disappointed at all," Zarif said. "We are all on the same wavelength and that's important... actually I think we had a very good, productive three days and it's something we can build on to move forward," he added.

French Foreign Minister Laurent Fabius was the first to reveal the deal had failed, pre-empting the official announcement after the talks broke up.

Fabius had earlier raised concerns that the proposal did not go far enough to curb Iran's nuclear ambitions.

"The meetings in Geneva have made it possible to move forward, but we have not yet managed to conclude, because there are still some questions remaining to be dealt with," Fabius said.

He insisted that France wanted an agreement, despite claims from some officials that Paris had stymied efforts to reach a deal.

US Secretary of State John Kerry, who had cut short a Middle East tour to join the talks, said "significant progress" had been made.

"There's no question in my mind that we are closer now as we leave Geneva," he said, adding that Washington remained intent on ensuring Iran does not obtain a nuclear weapon.

"We came to Geneva determined to make certain that Iran does not acquire a nuclear weapon. That remains our goal," Kerry said.

After stretching into a third day on Saturday, talks had continued into the early hours of Sunday, with Zarif joining ministers from the six powers for a last-ditch effort.

The P5+1 group includes the five permanent members of the UN Security Council -- Britain, China, France, Russia and the United States -- plus Germany.

The purported draft deal on the table could have seen Iran freeze parts of its nuclear programme in exchange for the easing of some of the sanctions that have battered its economy.

The world powers in the talks suspect Iran's programme is aimed at developing nuclear weapons, despite Tehran's repeated denials.

Iranian President Hassan Rouhani -- whose election is widely credited with kickstarting the nuclear talks -- had urged world powers not to miss the chance for a deal.

"I hope that the P5+1 group make the most out of this exceptional opportunity that the Iranian nation has offered to the international community, so that we can reach a positive result within a reasonable timeframe," he was quoted as saying by the official IRNA news agency.

Reports said the proposed deal could have seen Iran stop enriching uranium to 20 percent, which is just a few technical steps from weapons-grade, reduce existing stockpiles and agree not to activate its plutonium reactor at Arak.

Global powers would have in exchange taken limited and "reversible" measures to ease sanctions, such as unfreezing some Iranian funds in foreign accounts.

Negotiators would then have had time to work out a more comprehensive deal that Iran has said it hopes could be in place within a year.

The possible agreement had already come under fire from Tehran's arch-foe Israel, widely thought to be the Middle East's sole if undeclared nuclear armed power, which has opposed any move to ease sanctions.

"This is a very bad deal. Israel utterly rejects it," said Israeli Prime Minister Benjamin Netanyahu.

After years of fruitless efforts, talks over Iran's atomic activities were given new momentum by the June election of Rouhani, seen as a relative moderate.

Iran is anxious for relief from crippling US and European Union economic sanctions that have cut oil revenues by more than half, caused the value of its currency to plunge and pushed inflation above 40 percent.