Iran and world powers on Friday failed to reach a breakthrough in the Iranian nuclear crisis during talks that saw Tehran being criticised for failing to give a clear response to a proposal aimed at breaking the deadlock.
The powers are seeking answers about a nuclear programme that Iran insists is peaceful but world powers fear may hide some military dimensions.
The onus is now on Iran to accept a series of demands that include curbing enrichment activities in exchange for concessions which would ease UN sanctions that have choked the Iranian economy and seen its currency's value plummet.
Iran said its chief negotiator Saeed Jalili opened the negotiations in the Kazakh city of Almaty with goodwill by presenting a three-point outline of its own vision for how the dispute may be resolved.
"At this morning's meeting, his excellency Dr. Jalili presented specific plans and proposals for starting a new round of cooperation between Iran" and the world powers, his deputy Ali Bagheri told reporters after the first plenary session wound down after three hours.
But Western officials said the plan was just a rehash of old ideas that had already been cast aside at a meeting last year in Moscow.
"There has not yet been a clear and concrete response to the E3+3 Almaty I proposal" that the powers made at the last nuclear negotiations at the same venue in February, a Western official said in a statement to AFP also backed by a second source.
"Their presentation was pretty much a repetition of what they put forward in Moscow. There were some not fully explained general comments on our ideas," said the official on condition of anonymity.
The day's second plenary session ended after nearly three hours with the two sides at least agreeing to meet for another plenary session on Saturday.
Iran's Bagheri said Jalili presented "detailed" answers to a list of questions from the world powers.
"The answers prompted more questions," Russian news agencies quoted chief Russian negotiator Sergei Ryabkov as saying.
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"But this proves that these talks are serious," he added.
The last meeting at the same venue in February ended with unusual expressions of cautious optimism from both sides. Iran described those negotiations as "positive" while the world powers more coolly called them "useful".
But Jalili defiantly indicated going into Friday's session that Tehran had no intention of giving ground on the most important concession demanded by the West.
He told the six powers -- comprised of the five permanent UN Security Council members and Germany and known collectively as the P5+1 -- that Iran demanded an immediate recognition of his country's right to enrich uranium.
"We think that they can open up tomorrow's (Friday's) talks with one phrase -- and that is to accept Iran's right, particularly its right to enrich," Jalili said in a speech Thursday at an Almaty university.
The demand is inherently objectionable to the powers because Iran is prohibited from enriching uranium by the United Nations and is heavily sanctioned for its secretive work.
Jalili also appeared to downplay the chances of his one-on-one meeting with chief US negotiator Wendy Sherman -- talks Washington has been seeking for years.
An EU spokesman said decisions about bilateral meetings would be made as the talks progressed and refused to speculate about the reported possibility of dinner talks Friday between Jalili and EU foreign policy chief Catherine Ashton.
Failure to strike a compromise could prove costly to both sides. A possible war would likely see a global spike in oil prices and draw in other regional powers at an already unstable time in the Middle East.
Israeli Prime Minister Benjamin Netanyahu for one warned this week that "we cannot allow" the talks to drag on indefinitely while Iran continues to pursue enrichment.
The P5+1 grouping is particularly concerned about Iran's enrichment to levels of up to 20 percent and the Fordo fortified bunker where such activity is conducted.
They also want Iran to ship out its existing stockpile of 20-percent enriched material.