Iran is reported to be expanding its nuclear enrichment program even as major powers work to draw up sanctions against Tehran.
Diplomats in Vienna, insisting on anonymity, have told news agencies that Iran has tested a second enrichment facility. The sources say the test was a dry run and did not actually produce enriched uranium.
A spokesman for the UN's nuclear watchdog, The International Atomic Energy Agency in Vienna refused to comment.
Iran announced in April that it had resumed nuclear enrichment, which can be used to generate electricity or create an atomic weapon, depending on the level of enrichment.
As major powers move toward a UN sanctions resolution, Russia's foreign minister Sergei Lavrov said Moscow hopes Iran will return to negotiations over its nuclear program.
In Iran, President Mahmoud Ahmadinejad again said his country will not retreat over its nuclear program.
Talks between the European Union and Tehran broke down after Iran refused to suspend nuclear enrichment. Iran has defied an August 31 United Nations deadline to suspend its controversial activities.
A draft resolution, calling for limited sanctions against Iran, is expected to be submitted soon to the U.N. Security Council.
Western nations, led by the United States, accuse Iran of seeking to develop nuclear weapons. Iran says its nuclear program is for peaceful purposes.
Russia and China, which both have veto power in the U.N. Security Council, have resisted calls for tough penalties against Iran.
Some information for this report was provided by AFP and AP.