The operations at the bunker-like facility south of Tehran, reported Sunday by the Kayhan daily newspaper, are small in comparison to Iran’s main enrichment site. But the centrifuges at the underground labs are considered more efficient and are shielded from aerial surveillance and protected against airstrikes by up to 300 feet (90 meters) of mountain rock.
Uranium enrichment is at the core of the international standoff over Iran’s nuclear program. The U.S. and its allies fear Iran could use its enrichment facilities to develop high-grade nuclear material for warheads.
Iran — which claims it only seeks nuclear reactors for energy and research — has sharply increased its threats and military posturing against stronger pressures, including U.S. sanctions targeting Iran’s Central Bank in attempts to complicate its ability to sell oil.