The U.S. and its European allies want a "substantive" response from Iran when nuclear talks resume in Kazakhstan on Friday which signals Tehran's readiness to take serious steps to allay concerns about its nuclear ambitions, senior diplomats said. The talks, likely to continue until Saturday afternoon in Kazakhstan's most populous city, will be the first indication of whether February's sweetened offer by six major powers is enough to convince Iran to suspend its enrichment of uranium to 20% purity and take other steps to demonstrate its nuclear program is for peaceful purposes
The U.S. and its European allies want a "substantive" response from Iran when nuclear talks resume in Kazakhstan on Friday which signals Tehran's readiness to take serious steps to allay concerns about its nuclear ambitions, senior diplomats said.

The talks, likely to continue until Saturday afternoon in Kazakhstan's most populous city, will be the first indication of whether February's sweetened offer by six major powers is enough to convince Iran to suspend its enrichment of uranium to 20% purity and take other steps to demonstrate its nuclear program is for peaceful purposes.

February's offer from the P5+1 group, the five permanent members of the United Nations Security Council plus Germany, offered Iran additional sanctions relief if Tehran agrees to what was billed as an confidence-building deal. The move placed the onus squarely on Iran to make the next move.

On Thursday, hours ahead of the talks, Iranian officials sought to deflect pressure and place the onus back on the P5+1. Speaking to a roomful of students and reporters in one of Almaty's leading universities, Mr. Jalili said talks could progress this week but only if the U.S. and its allies accept Iran's "right" to enrich uranium.

"By using a single word, [the talks] can find their way forward," he said. "That word is acceptance of rights of the Iranian people, especially its rights of enrichment."

Calling this a major "test" of the P5+1's sincerity, Mr. Jalili said "Are they going to accept that right or are they going to try to deny that right to the Iranian people?"

Iran has long demanded the P5+1 recognize its right to enrich but has rarely tied it so clearly to an apparent willingness to make clear concessions of its own.

As a signatory of the Nuclear Non-proliferation Treaty, Iran had a right to enrich uranium for a peaceful nuclear program. But after hiding an enrichment program for 18 years in breach of the treaty, the United Nations Security Council has passed half a dozen resolutions since 2006 demanding Tehran suspend enrichment until it proved its nuclear activities were for civilian purposes.

In the past, Western officials have said Iran could eventually win the right to enrich uranium for a peaceful nuclear program. The fact that recent talks have focused on Iran's enrichment up to 20% purity--considered only a short technical step from weapons grade--has reinforced the sense that the West could live with lower-purity enrichment. However, officials have said any formal acknowledgment of this must be conditional on Tehran restoring confidence in its nuclear plans.

After Mr. Jalili's speech, an Iranian diplomat said Tehran was "open to" most of the demands made by the P5+1 in February but a public acknowledgment of Iran's enrichment rights must come upfront.

Western diplomats warned Iran would be unwise to place further hurdles in the way of a possible deal.

With the Iranian presidential elections looming and President Barack Obama saying last month that Iran was "over a year or so" from being able to develop nuclear weapons, western diplomats had tempered expectations of any major breakthrough in Almaty--the second meeting in a row in this mountain-ringed city in the south of Kazakhstan.

EU foreign policy chief Catherine Ashton, who chairs the P5+1, said during a press conference in Ankara on Wednesday that after "useful" technical talks in Istanbul on March 18 with Iran, she was "ready now to hear formally the response from Iran.

"I remain always cautiously optimistic but I'm also very clear that it is very important we do get a response," she said.

That view was echoed by a senior U.S. official late Wednesday.

"There has been some ... meeting momentum generated over the past month or so, and we are prepared to engage with the Iranians," the person said. "But how far we get in Almaty ... depends on what the Iranians come back with in terms of a response on the substance to our proposal," the person said. "We hope Iran comes prepared, makes a substantive and concrete response."

In its February proposal, the P5+1 called on Iran to suspend its 20% enrichment, remove most of its stockpile of already produced 20% enriched uranium and stop activities at Fordow, a fortified underground military facility in the holy city of Qom. It had previously called for Fordow to be closed and for all higher enriched uranium to be taken out of Iran.

In exchange, Iran could see sanctions lifted on its petrochemical sector and would be allowed to renew trade in gold and precious metals--a move that would have eased the tight financial restrictions the U.S. and Europe have placed on the country. There would also be no fresh sanctions push over Iran's program. Mr. Jalili called the new proposal "positive" in February.

With sanctions biting and the Iranian elections approaching, senior western officials have said recently they think Iran's Supreme Leader Ayatollah Ali Khamanei has for now decided to keep the country's nuclear program within the "red lines" demanded by Israel.

According to the International Atomic Energy Agency, Iran has kept its stockpile of uranium enriched to 20% purity to well below 250 kilograms--enough to produce one atomic bomb. It has done so by converting some of the stockpile into fuel plates to power Tehran's research reactor. Fissile material in this form is difficult to use in a weapons program, U.S. and European officials say.

Mark Fitzpatrick, director, Non-Proliferation and Disarmament Program, of the Institute for International Strategic Studies in London, said while no breakthrough is "on the cards" this week, some "real negotiations" were at least possible.

"To date the meetings have been presentations of positions without any real engagement in terms of counteroffers, so in a sense they have been talking past one another," he said. "If they do--and it's a real proposal unlike the one Iran presented last summer ... then that's a positive development and represents a small ray of light."