Secretary of Supreme National Security Council Saeed Jalili on Wednesday sent a letter to EU foreign policy chief Catherine Ashton saying that the EU's failure to arrange a meeting of experts to draft an agenda for the talks created an atmosphere of doubt and ambiguity for the Moscow talks.

Russia is hosting the third round of talks on Iran’s nuclear program June 18-19.

“The Islamic Republic of Iran… wants to advance the nuclear talks,” Jalili said, adding that talks just for the sake of talks “are not useful” and expressing hope that an agenda could still be drafted.

The United States has warned it will tighten sanctions against Iran if the Moscow negotiations fail to make progress on the Islamic Republic's nuclear program.

“If we don't get a breakthrough in Moscow there is no question we will continue to ratchet up the pressure," David Cohen, U.S. Treasury undersecretary for terrorism and financial intelligence, said. "The sanctions are having an impact on Iran, but I also recognize that more needs to be done. And we are intent on doing more.”

The previous round of Iran Six talks was held in Baghdad on May 23-24.

Western nations and Israel are seeking to persuade Iran to give up its uranium enrichment program, which they suspect is aimed at producing nuclear weapons. Iran says its nuclear program is merely designed to generate energy.