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.”