VIENNA (AP) -- Iran nuclear talks stalled Friday, casting a shadow on earlier advances and denting hopes that Tehran and six world powers will meet a July 20 target date for a deal meant to curb Iran's atomic program while ending sanctions on the Islamic Republic.
Deputy Iranian Foreign Minister Abbas Araghchi acknowledged the meeting made "no progress" in its ambitious goal of starting to draft an agreement meant to ease a decade of Western distrust about Tehran's nuclear agenda in exchange for sanctions relief.
In that, "we failed," he told reporters. But while saying he was disappointed, he insisted that the result of the three-day talks that ended Friday represented no more than a setback at this point in continuing attempts to reach a deal.
A senior U.S. official -- who demanded anonymity under U.S. briefing rules -- said there was "great difficulty" in trying to move toward common positions and spoke of "significant" differences. Both Araghchi and the official said further meetings were planned in June, but no dates were announced.
The failure to advance diminished a sense of optimism that had been growing since talks began Feb. 18 on a comprehensive deal. But while diplomats had spoken of some progress before the three-day round that ended Friday, they had also warned of difficult talks ahead on some issues, such as Iran's enrichment program.
Iran says it has no interest in nuclear arms, and wants to enrich only to make reactor fuel. But because the technology can also create weapons-grade uranium for warheads depending on the level of enrichment, Washington and its allies want strict constraints on its size and scope.
The talks are being closely watched by Israel for signs that Tehran is using them as a cover while trying to reach the ability to make a nuclear weapon -- something the Jewish state has vowed to prevent by any means, including force.
While saying diplomacy is the best path, Washington has said all options remain on the table to prevent a nuclear-armed Iran. In Jerusalem Friday, U.S. Defense Secretary Chuck Hagel told Israeli leaders that the U.S. "will do what we must" to ensure that goal.
Araghchi said that differences remained on more than a dozen issues and a Western official with detailed knowledge of the talks said that enrichment was among the most divisive topic.
The official declined to go into the specifics of what separated the two sides on enrichment and demanded anonymity because he wasn't authorized to discuss the confidential talks.
But general differences have long been known. Iran's nuclear chief, Ali Akbar Salehi, has said publicly that Tehran needs up to 100,000 centrifuges -- the enriching machines -- for a future nuclear network.
That's about five times as many as the centrifuges Iran now has standing but idle, 10 times that of the machines actually enriching -- and much more than the few thousand that diplomats say the U.S. and its allies are prepared to allow.
Related differences focus on length of constraints on enrichment and other nuclear activities that could be proliferation-relevant. The diplomats say the U.S. and other Western countries want decade-long limits, whereas Tehran is pushing only for a few years before all restrictions are lifted.
Other disagreements include how -- or whether -- the talks should also focus on Iranian missiles capable of delivering a nuclear warhead and suspicions that Tehran worked secretly on trying to make atomic arms -- allegations the Islamic Republic denies.
Diplomats said before this week's round that there was tentative agreement on some topics, including rough consensus on the need to re-engineer a partially built reactor so that it would produce less waste plutonium -- material that also can be used for the core of a nuclear weapon.
They also said Iran is ready in principle to sign an agreement with the U.N. atomic agency that would allow its experts to visit any declared nuclear site at very short notice, investigate suspicions of undeclared nuclear activity and push for deeper insight into all atomic work.
But Araghchi's remarks indicated that the devil was in the detail of putting any general ideas on what needed to be done into the form of a precisely worded unambiguous text.
And he suggested more discussion might be needed between his country and the six -- the United States, Russia, China, Britain, France and Germany --before drafting actually began. Such delays could push negotiations past the July 20 target date, but the two sides have agreed they could be extended by up to six months if needed.
"In previous rounds of negotiations we only had brainstorming sessions," he said. "The goal of this round was to draft an agreement (and) we feel that differences are still there. And we should wait for the time when ... the positions are closer."
Margaret Childs in Vienna, and Nasser Karimi in Tehran, contributed to this report.
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