Iran has confirmed it has started uranium enrichment at a second facility where the material can be upgraded quickly for potential use in a nuclear bomb.
Iran's envoy to the International Atomic Energy Agency (IAEA) said Monday that Tehran is refining uranium at the newly-launched Fordo complex and an older facility in the city of Natanz. Ali Asghar Soltanieh said it was taking place under the supervision of the IAEA. He made his comments to Iran's Arabic language al Alam TV network.
The U.N. Security Council has imposed four sets of sanctions on Iran for refusing to stop enrichment work, which has civilian and military uses. Western powers accuse Iran of trying to develop an atomic weapons program. Tehran says its nuclear ambitions are peaceful.
The United States and the European Union have been tightening their own sanctions on Iran to pressure it into suspending enrichment. Iranian Supreme Leader Ayatollah Khamenei said Monday the sanctions will not achieve their goals and vowed to resist the pressure. His remarks were broadcast on state television.
Earlier Monday, diplomats with ties to the IAEA also confirmed that Iranian centrifuges have begun refining uranium to a purity of 20 percent at Fordo, an underground complex near the Shi'ite holy city of Qom.
The Fordo complex is located beneath a mountain and is better protected from potential airstrikes by nations opposed to the Iranian nuclear program. Iran said previously it was preparing to move its highest-grade enrichment work to Fordo from its an above-ground plant in Natanz.
Most of the work at the Natanz facility has involved refining uranium to a relatively low purity of 3.5 percent. Enrichment to the 20 percent level at the Fordo complex could reduce the time needed for Iran to further refine the material to the 90 percent purity required for nuclear weapons.
Iran says its nuclear program is designed only to generate electricity and material for medical research.
The United States and its ally Israel have not ruled out military action to stop the program. Israel sees a nuclear-armed Iran as a threat to the Jewish state's existence.
In a television interview broadcast Sunday, U.S. Defense Secretary Leon Panetta said Iran's nuclear program has not progressed to the stage of building a nuclear bomb. But he warned Iranian leaders that if they take such a step, the United States will stop them.
Panetta said Washington will continue what he called a "responsible" approach of putting diplomatic and economic pressure on Iran to abstain from developing nuclear weapons. He also advised Israel not to take unilateral action against Iran, saying a "better approach" is to "work together" with the United States on the issue.
Some information for this report was provided by AfP and Reuters.