Iran on Sunday hit out at a perceived lack of willingness by world powers to engage it ahead of crucial nuclear talks to take place in Moscow on June 18 and 19, according to reports.
Ali Bagheri, deputy to Iran's top negotiator Saeed Jalili, said in a letter to Helga Schmid, deputy to EU foreign policy chief Catherine Ashton, that he was "surprised" by issues she was raising in correspondence with him.
He also complained that preparatory groundwork by experts from both sides was needed before the talks.
The letter, whose Farsi translation was made public by several Iranian news agencies, showed the gulf that exists between Iran and the so-called P5+1 group (the United States, Britain, France, Germany, Russia and China) going into the negotiations.
Ashton's office represents the P5+1 in dealings with Iran.
Bagheri and Schmid are tasked with arranging the talks and have exchanged several letters. The Moscow round follows two earlier meetings since early April, in Istanbul and in Baghdad, that have failed to yield any progress.
Bagheri wrote to Schmid: "Your recent letter surprised me; it tabled issues that were a long way apart from the agreements... of the talks in Baghdad between Iran and the P5+1 as well as those agreed in comprehensive talks between the deputies in Geneva."
He said that Schmid had "neither introduced any plans nor responded to the proposals of the Islamic Republic of Iran" that were presented in Baghdad as a counter-offer to a P5+1 package of demands and incentives that Iran rejected.
Bagheri also asked why Ashton's office was refusing an Iranian request that the Moscow round be preceded by a meeting of experts and deputies to define its scope and agenda.
"Will the upcoming talks be successful, with an agenda with defined dimensions, or will it be successful only for the sake of talks-for-talks and without an agenda?" he wrote.
"If the agreements of each round of talks cannot be followed up at the level of deputies and experts, what guarantee will there be for the success of future talks?"
Bagheri said, however, that "Iran is ready for successful talks to be held, following a clear logic and specified proposals. I hope you can also find this readiness."
A letter by Schmid to Bagheri, obtained by AFP last Thursday, stressed that the P5+1 was focused on its own package of proposals.
"Now there is a need to engage seriously on issues of substance in order to agree on concrete confidence building steps which could be implemented swiftly. We are very much hoping for a political commitment on your side," Schmid wrote.
The Western nations in the P5+1, and the International Atomic Energy Agency, have suspicions that Iran has conducted research towards developing nuclear weapons.
Iran denies that accusation and claims it is being unfairly treated by the West under the terms of the nuclear Non-Proliferation Treaty.