GENEVA — World powers’ efforts to reach a nuclear agreement with Iran adjourned early Sunday with both sides speaking of progress but with failure to seal a deal that both sides badly wanted — initial caps on Tehran’s ability to make an atomic bomb in exchange for some easing of sanctions stifling Iran’s economy.

As the talks foundered after optimistic words of progress from both sides, U.S. Secretary of State John Kerry rushed to Geneva, followed by counterparts from Russia, China, Britain, France and Germany, for a last-ditch effort to muscle through an accord.

That push failed, with Iranian opposition to giving too much for too little in return complicated by dissent within the six powers. France rejected a joint list of demands on Iran, saying they were too generous to result in sanctions relief.

Top EU diplomat Catherina Ashton joined Iranian Foreign Minister Mohammad Javad Zarif to announce progress, but no conclusive results. Talks that began Thursday and spilled into early Saturday with a final joint meeting between negotiators of both sides.

Ashton spoke of ‘’a lot of concrete progress” but also of ‘’some differences.” Zarif said he hoped those disagreements will be resolved at a future meeting. The two said they would talk on Nov. 20, but no full new round between the two sides was announced.

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.”

He did not elaborate, but it appeared France wanted tougher constraints on a reactor that will make plutonium when completed and also on parts of Iran’s uranium enrichment program.

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.

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 440 pounds (200 kilograms) of higher-enriched uranium in a form that can be turned into weapons much more quickly. Experts say 550 pounds (250 kilograms) of that 20 percent-enriched uranium are needed to produce a single warhead.