DUBAI - Iran's supreme leader criticized Western powers on Thursday for not offering concessions in talks last week, saying the West was using the nuclear issue as a pretext to impose sanctions and harm the Islamic Republic.

It was Ayatollah Ali Khamenei's first reaction to what Iranian officials described as "positive" nuclear talks in Almaty, Kazakhstan, during which the P5+1 group of nations offered modest sanctions relief in return for Iran curbing higher grade uranium enrichment.

"Western nations did not accomplish anything that can be construed as a concession, and instead they admitted Iran's rights only to a degree," Khamenei said in an address reported on his official website.

"To assess their integrity, we must wait until the next round of talks," he added.

Khamenei said the West was using Iran's nuclear program as a "pretext" to impose sanctions and pressure Iranians to "confront the system."

After the talks ended last Wednesday, Iran's chief nuclear negotiator Saeed Jalili said the P5+1 - United States, China, France, Russia, Britain and Germany - had tried to "get closer to our viewpoint" and said he believed the meeting could be "a turning point."

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Western officials said the offer presented by the six powers included easing a ban on trade in gold and other precious metals, and a relaxation of an embargo on Iranian petrochemical products. They gave no further details.

In exchange, a senior US official said that Iran would, among other things, have to suspend uranium enrichment to a fissile concentration of 20 percent at its Fordow underground facility and "constrain the ability to quickly resume operations there."

Iran maintains it has the right to enrich uranium, both for nuclear power plants and for making medical isotopes which requires fuel enriched to a fissile purity of 20 percent.

But the US and its allies are concerned that 20-percent purity is a major step towards producing weapons-grade uranium and that Tehran is covertly developing weapons capability, accusations Iran denies.

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