ALMATY, Kazakhstan -- Iran and six world powers failed to reach agreement Saturday on how to reduce fears that Tehran might use its nuclear technology to make weapons, extending years of inconclusive talks and adding to concerns the diplomatic window on reaching a deal with Tehran may soon close.
Expectations the negotiations were making progress rose as an afternoon session continued into the evening. But comments by the two sides after they ended made clear that they fell far short of making enough headway to qualify the meeting as a success.
"What matters in the end is substance, and ... we are still a considerable distance apart," Catherine Ashton, the European Union's head of foreign policy, told reporters at the end of the two-day talks.
Ms. Ashton, the convener of the meeting, said negotiators would now consult with their capitals. She made no mention of plans for new talks -- another sign that the gap dividing the two sides remains substantial. She said she would talk with chief Iranian negotiator Saeed Jalili by telephone over further steps.
Mr. Jalili spoke of "some distance between the positions of the two sides." He suggested Iran was ready to discuss meeting a key demand of the other side -- cutting back its highest-grade uranium enrichment production and stockpile -- but only if the six reciprocated with rewards far greater than they are now willing to give.
Western negotiators noted an improved atmosphere from previous sessions, with Ms. Ashton speaking of "a real back and forth between us when were able to discuss details, to pose questions, and to get answers directly."
Still, the lack of forward movement in international negotiations that started a decade ago was certain to increase concerns that diplomacy was ineffective as a tool to stop Iran from moving toward nuclear-weapon making capacity.
Israel is most worried. The Jewish state says Iran is only a few months away from the threshold of having material to turn into a bomb and has vowed to use all means to prevent it from reaching that point. The U.S. has not said what its "red line" is, but has said it will not tolerate an Iran armed with nuclear weapons.
Any strike on Iran could provoke fierce retaliation directly from Iran and through its Middle East proxies in Syria, Lebanon and Palestine, raising the specter of a larger Middle East conflict and adding to the urgency of keeping both sides at the negotiating table.
At the talks in the Kazakh city of Almaty, the U.S., Russia, China, Britain, France and Germany were asking Tehran to greatly limit its production and stockpiling of uranium enriched to 20 percent, which is just a technical step away from weapons-grade uranium. That would keep Iran's supply below the amount needed for further processing into a weapon.
But the group views that only as a first step in a process. Iran is operating more than 10,000 centrifuges. While most are enriching below 20 percent, this material, too could be turned into weapons-grade uranium, although with greater effort than is the case for the 20-percent stockpile.
Tehran also is only a few years away from completing a reactor that will produce plutonium, another pathway to nuclear arms.
The lack of progress at Almaty was a clear indication that Tehran wants greater rewards for any concessions that the six are ready to give. Among other incentives, they have offered to lift sanctions on Iran's gold transactions and petrochemical trade. But Iran demands much more substantial sanctions relief, including an end to international penalties crippling its oil trade and financial transactions.