Report: Iran enriching uranium underground

TEHRAN -- Iran has begun uranium enrichment at a new underground site built to withstand possible airstrikes, a leading hard-line newspaper reported Sunday in another show of defiance against Western pressure to rein in the nuclear program.

The operations at the bunkerlike facility south of Tehran, reported by the daily newspaper Kayhan, are small, compared with 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 of mountain rock.

In an interview broadcast Sunday, U.S. Defense Secretary Leon Panetta said Iran is laying the groundwork for making nuclear weapons someday, but is not yet building a bomb. He reiterated U.S. concerns about a possible unilateral strike by Israel against Iran's nuclear facilities, saying that could trigger Iranian retaliation against U.S. forces in the region.

Uranium enrichment is at the core of the international standoff over Iran's nuclear program. The United States and its allies fear Iran could use its enrichment facilities to develop high-grade nuclear material for warheads.

Iran, which claims it seeks nuclear reactors only for energy and research, has increased its threats and military posturing against stronger pressures.

A senior commander of the Revolutionary Guard force was quoted as saying Tehran's leadership will order the Strait of Hormuz, a strategic oil route, closed if the country's petroleum exports are blocked.