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.

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.

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 Ashton speaking of “a real back and forth between us when were able to discuss details, to pose questions, and to get answers directly.”

She described the better negotiating climate as a “very important element.”

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.

“The Iranians are using the round of talks to pave the way toward a nuclear bomb,” said Yuval Steinitz, the Israeli minister for intelligence and strategic affairs, in a text message to reporters. “Israel has already warned that the Iranians are taking advantage of the rounds of talks in order to buy time to advance in uranium enrichment, step by step, toward a nuclear weapon.”

Urging the international community to set a “short, clear and final timetable” for further talks, he said “the time has come for the world to show a more aggressive position and make it abundantly clear to the Iranians that their game of negotiations is coming to an end.”

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 U.N. Security Council has demanded a stop to both that effort and all enrichment in a series of resolutions since 2006. Iran denies any interest in atomic arms, insists its enrichment program serves only peaceful needs, says it has a right to enrich under the Nuclear Nonproliferation Treaty and describes U.N. Security Council demands as illegal.

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

A senior U.S. official cited Iranian officials who described the six-power offer of limited sanctions relief in exchange for meeting their demands on 20-percent uranium as a “turning point” when the two sides met last month. The official said the U.S. administration was “disappointed that this rhetoric did not carry over into our negotiations.”

The official demanded anonymity as a condition for participation in a post-meeting briefing for reporters.

Jalili in turn urged the six powers to demonstrate their “willingness and sincerity” by taking appropriate confidence-building steps in the future” _ shorthand for Iran's demand to lift major sanctions and offer other concessions.

At the same time, he suggested some potential give on the Iranian side, suggesting discussion on some curbs of 20-percent enrichment “can be continued in the talks” if the six “move away from hostile treatment ... of the Iranian people.”

With Iran previously describing the crushing sanctions on its oil exports and financial transactions as hostile acts, his comments suggested that Iran would consider compromise only if those penalties were lifted. That is far more than the relief being offered, with the six prepared to remove sanctions only on Tehran's gold transactions and petrochemical exports.

In demanding recognition of its right to enrich, Iran may hope to exploit some differences among the six, with Russia in recent months pushing for concessions on that point as a way to break negotiating deadlock.

Russian Deputy Foreign Minister Sergei Ryabkov, who led his country's delegation at Almaty, said after the talks that Moscow “considers that it's necessary to recognize all rights of Iran, including enrichment.” In exchange, he said Iran must accept more international monitoring of its nuclear program.

A British Foreign Office statement said “a wide gap remains between the parties. Iran's current position falls far short of what is needed to achieve a diplomatic breakthrough.”

Indirectly warning of further sanctions, the statement urged Tehran to “consider carefully whether it wants to continue on its current course, and face increasing pressure and isolation from the international community, or to enter into meaningful negotiations.”

But Ryabkov described the meeting as “undoubtedly a step forward.” Those remarks, and his comments on enrichment, both to Russian news agencies, suggested differences exist among the six, despite assertions by negotiators from Western nations of total unity at the negotiations. (AP)