ALMATY, Kazakhstan -- Negotiations over Iran's disputed nuclear program broke off Saturday with scant signs of progress, much less an agreement on tighter controls demanded by six world powers in exchange for some easing of sanctions that have a stranglehold on the Iranian economy.
The failure to reach any accord was a stark but not surprising setback in a tortuous, decade-long standoff over Iran's nuclear ambitions. While the talks have been complicated by the Iranian presidential election just 10 weeks away, officials said the sides remained divided by fundamental disagreements, none of which are new.
Catherine Ashton, the European Union's foreign policy chief, who led the talks for the six powers, said that after two days of "long and intense discussions," the sides "remain far apart on the substance."
No future negotiations were announced, and Ms. Ashton said she would be "in touch very soon" with the top Iranian negotiator, Saeed Jalili, "in order to see how to go forward."
Mr. Jalili offered a sharply different summary, saying at a briefing that the next move was up to the big powers, and that they needed more time to digest a new proposal from Iran. He said the proposal was largely based on a plan first put forward in Moscow in June and aimed at addressing some of the international community's concerns.
But he also adopted a strident tone in reiterating Iran's view that it has a right to enrich uranium for civilian purposes.
"Of course, there is some distance in the position of the two sides," Mr. Jalili said. But he said Iran's proposals, which required recognizing "our right to enrich and ending behaviors which have every indication of enmity toward the Iranian people," were designed "to help us move toward a constructive road."
A senior American official called Iran's demands were unreasonable and "disproportionate."
"It is fair to say that Iran is prepared to take very minimal steps in regards to its nuclear program," said the official, who spoke on the condition of anonymity, which has become the State Department's standard practice at the talks.
The official insisted that the Obama administration was still committed to achieving a diplomatic solution, but warned of additional sanctions should Iran fail to voluntarily curb its nuclear program. "International pressure continues and will only increase if Iran is not responsive," the official said.
Britain also warned of tougher sanctions. "Iran's current position falls far short of what is needed to achieve a diplomatic breakthrough," Foreign Secretary William Hague said in a statement. He added, "We look to Iran to consider carefully whether it wants to continue on its current course, and face increasing pressure and isolation from the international community."
Officials struggled to give a realistic assessment of the talks' failure, while also offering a hint of optimism.
"There may not have been a breakthrough but there also was not a breakdown," the American official said." Sergei Ryabkov, Russia's lead negotiator, said, "We're still on the threshold," according to the Interfax news service.
The futility of the talks was certain to arouse renewed alarm, particularly from Israel, which had tempered its repeated threats of a military strike against Iranian nuclear sites in deference to the diplomatic efforts.
"This failure was predictable," Yuval Steinitz, Israel's minister of strategic affairs, said in a statement. "Israel has already warned that the Iranians are exploiting the talks in order to play for time while making additional progress in enriching uranium for an atomic bomb." He added, "The time has come for the world to take a more assertive stand and make it unequivocally clear to the Iranians that the negotiations games have run their course."
The conclusion of the talks without agreement on even a modest confidence-building measure or the clear prospect of future talks was striking given that all sides seemed to have incentives to keep the conversation going, and to avoid talk of military intervention.
The United States has focused increasingly in recent weeks on an intensifying threat from North Korea, which, unlike Iran, already possesses nuclear weapons. Iran, meanwhile, is preoccupied by an internal power struggle over the presidential election.
Western countries fear that Iran is trying to develop nuclear weapons, while Iran has insisted that its program is for peaceful purposes, including atomic energy and medical research, to which it claims a right as a signer of the Nuclear Nonproliferation Treaty.
Iran has accused the big powers, particularly the United States, of hypocrisy for maintaining their own nuclear arsenals. But at the same time, Iran has refused to comply with United Nations Security Council demands that it suspend its uranium enrichment program, expand access for inspectors and answer questions about its intentions.
The talks here in Kazakhstan were the fifth round over the past year between Iran and the so-called P5-plus-1. The group consists of the five permanent members of the Security Council -- Britain, China, France, Russia and the United States -- plus Germany.
The negotiations have settled into a familiar routine: the big powers demand concrete steps from Iran and a firm commitment to comply with United Nations and other international mandates, only to be faced with delays or complicated counterproposals, including one on Friday that one Western diplomat said had left officials "puzzled."
Western officials had arrived here with guarded optimism that Iran would give a concrete response to a February proposal that would provide a modest easing of sanctions in exchange for restrictions on Iran's supply of enriched uranium. Enriched to high levels, the uranium could be used in nuclear weapons.
The proposal called for Iran to accept broad oversight for all of its nuclear activities by the International Atomic Energy Agency, but the big powers dropped a demand that Iran shut its enrichment plant at Fordo, built deep below a mountain. Instead, Iran would only have to suspend enrichment there, and take other steps that would make it difficult to resume quick production of nuclear fuel.
In another apparent softening, the six powers had said Iran could keep a small amount of uranium enriched to 20 percent purity, which can be converted relatively quickly to weapons grade, for use in a reactor to produce medical isotopes.
After the first morning of discussions on Friday, the Iranians said they had offered a new "comprehensive" proposal aimed at building cooperation. The statement baffled the six powers, who said they had not heard anything that sounded like a new plan. The Iranian side later clarified that it had presented a "scaled down" version of a package first proposed in Moscow in June, which was quickly rejected.
Mr. Jalili said Saturday that Iran's plan incorporated the proposal put forward in February, and said the next move was up to the six powers. "Good negotiations took place, and in consideration of our new proposals, it is now up to the P5-plus-1 to demonstrate its willingness and sincerity to take appropriate confidence building steps in the future," he said.
Ms. Ashton and Mr. Ryabkov agreed that there had been somewhat more productive give-and-take than in previous meetings.
"The Iranians' position was quite open and quite constructive," Mr. Ryabkov said. Still both diplomats said that ultimately the sides were too far apart on the substantive issues.
Jodi Rudoren contributed reporting from Jerusalem.
This article originally appeared in The New York Times.