DUBAI - Iran's deputy negotiator said world powers were unprepared for the next round of talks over the Islamic Republic's disputed nuclear program and had failed to honor agreements reached in previous negotiations, Iranian media said on Sunday.

The comments - made in a letter from Ali Bagheri to his European counterpart - are the latest volley in an apparently escalating spat over preparations for the next round of meetings in Moscow on June 18-19.

Bagheri said Iran had previously made "specific" proposals regarding a framework for further negotiations and their substance, but world powers were holding the process up.

"Despite the follow-ups and numerous letters from the Islamic Republic of Iran, until now you have not been able to demonstrate readiness," Bagheri wrote in response to a letter from the European Union's Helga Schmid.

"We hope that you will be able to find the preparedness as quickly as possible," Bagheri said in his letter, a copy of which was published by the Iranian Students' News Agency.

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At the heart of the dispute is Iran's desire to hold preparatory talks that include input from experts, but the P5+1 countries - comprising the United States, China, Russia, Germany, France and Britain - have indicated that all issues should be addressed in Moscow.

It is unclear what Iran hopes to gain from such preliminary talks. Western diplomats have often accused Tehran of seeking to buy time for its nuclear activities by trying to engage in talks about process rather than substance.

Schmid wrote to Tehran last week saying the P5+1 would insist on Iran curbing its production of high-grade uranium at the next round of nuclear talks in Moscow.

Schmid said in her letter she was "somewhat surprised" by Tehran's allegations and that world powers had shown readiness to hold in-depth discussions over their proposal, which would involve Tehran closing an underground enrichment facility and shipping out its stockpile of high-grade uranium.

Western nations suspect that the Islamic Republic's higher-grade uranium enrichment is part of a clandestine program to develop the material and components needed to be able to make nuclear arms, a charge Iran has repeatedly denied.

In his reply, Bagheri also expressed "surprise" at the content of Schmid's letter, which he said differed greatly from what they had agreed to at the previous round of talks in Baghdad, including the preparatory talks.

Last month US Secretary of State Hillary Clinton said Washington needed to see "concrete actions" from Iran.

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