VIENNA -- An ambitious round of nuclear talks between Iran and six world powers ended Friday with serious setbacks, with a senior Iranian official saying the two sides are at odds on several key issues.
Both sides were supposed to start drafting a final agreement that the six hope will constrain Iran's nuclear program. Tehran in turn is seeking a full lifting of sanctions.
But Iranian Deputy Foreign Minister Abbas Araghchi told Iranian media Friday that differences were too big to start the drafting process. He gave no immediate details beyond saying that both sides were apart on several issues.
"There was no tangible progress in this round of the talks," Araghchi said. "We will have one or two more rounds of talks in June. Talks will continue."
A senior U.S. official told Reuters that there needs to be "additional realism" in the talks and that time is not unlimited.
Talks began Feb. 18 on a comprehensive deal meant to constrain Iranian nuclear work that can make such arms in exchange for full sanctions relief on Tehran's economy. Araghchi said there was still hope a final deal can be reached before July 20, the target date for a comprehensive deal.
Iran denies any interest in nuclear weapons, saying its enrichment program is meant 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 dispute over enrichment surfaced less than two months before the July 20 target date for a deal and follows encouraging signs of progress on less contentious issues in earlier rounds that had raised hopes that a pact could be sealed by then.
Diplomats say there is a tentative agreement 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 say 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.
For Iran, the major sticking point is sanctions relief, reports CBS News correspondent Elizabeth Palmer.
President Obama's administration can offer to unblock tens of billions in frozen Iranian assets. However, the Iranians want more than that money. They want business links to the West, and access to the global banking system and financial markets.
Finally, the two sides fundamentally disagree on the length of time any comprehensive agreement would remain in effect, Palmer reports. The P5+1 are talking about decades, while Iran wants all restrictions lifted after a few years.
Trita Parsi, president of the National Iranian American Council, told Palmer that a long-term deal is unlikely.
"Iran will likely reject a deal that lasts beyond 10 to 15 years, not just because of the mistrust that exists between the two sides, but also because of the legitimate uncertainty that exists about the intentions and orientations of future leaders in Washington and Tehran." Parsi said.