Negotiator Ali Larijani said the United States' alleged insistence on referring Iran to the UN Security Council for possible punitive sanctions was making it impossible to reach agreement.
The latest round of talks in Moscow between Iran and Russia on a joint proposal to enrich Iran's uranium on Russian soil ended on March 1 without any visible breakthrough. There was no date given for the next round of talks.
The Russian proposal is widely seen as a compromise that would allow Iran to have a civilian nuclear program, while allaying international fears the country could be building a covert atomic weapon.
Reports say Larijani will meet in Vienna on March 3 with the foreign ministers of Britain, France, and Germany for further talks.
(AFP, AP, Reuters)