ALMATY, Kazakhstan -- Iran and six world powers failed to reach agreement Saturday on an approach to reducing fears that Tehran might use its nuclear technology to make weapons, with the EU's foreign policy chief declaring that the two sides "remain far apart on substance."

Expectations that the negotiations were making progress rose as an afternoon session was extended into the evening. But comments by the two sides made clear that they failed to make 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.

Ashton said negotiators would now consult with their capitals. She made no mention of plans for a new meeting - another sign that the gap dividing the two sides remains substantial.

Chief Iranian negotiator Saeed 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 concessions far greater than they are now willing to make.

Iran's 20 percent enriched uranium is just a step away from weapons-grade uranium. Stopping its production and shipping out most of it would keep Iran's supply below the amount needed for further processing into a weapon.

The six - the United States, Russia, China, Britain, France and Germany - say the Islamic Republic must meet its demand on 20 percent uranium, and make that move first, to build confidence that its nuclear program is peaceful.

But Iran wants greater rewards for any concessions that the six are ready to give. They have offered to lift sanctions on Iran's gold transactions and petrochemical trade. But Tehran wants much more substantial sanctions relief. It seeks an end to international penalties crippling its oil trade and financial transactions.

Jalili questioned that it was up to Iran to make the first step, saying it was up to the six powers to demonstrate their "willingness and sincerity." He urged them to "take appropriate confidence-building steps in the future" - shorthand for Iran's request to lift major sanctions and offer other concessions.

The talks already seemed to run into trouble shortly after they began Friday with a Western diplomat saying Iran's response to the offer from the group fell short of what the six wanted and instead amounted to a "reworking" of proposals it made last year at negotiations that broke up in disagreement.

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