Iran has begun uranium enrichment at a new underground site well protected from possible airstrikes, a leading hardline newspaper reported Sunday.

The announcement came as another newspaper quoted a senior commander in the country's powerful Revolutionary Guard as saying that Tehran's leadership has decided to order the closure of the strategic Strait of Hormuz if the country's oil exports are blocked.

Iran is under UN sanctions for refusing to stop uranium enrichment — which can produce both nuclear fuel and fissile warhead material — and other suspected activities that the international community fears could be used to make atomic arms.

Tehran says it only seeks reactors for energy and research, and refuses to halt its uranium enrichment activities.

Kayhan daily, which is close to Iran's ruling clerics, said Tehran has begun injecting uranium gas into sophisticated centrifuges at the Fordo facility near the holy city of Qom.

"Kayhan received reports yesterday that show Iran has begun uranium enrichment at the Fordo facility amid heightened foreign enemy threats," the paper said in a front-page report. Kayhan's manager is a representative of Iran's Supreme Leader Ayatollah Ali Khamenei.

But Iran's nuclear chief Fereidoun Abbasi said late Saturday that his country will "soon" begin enrichment at Fordo. It was impossible to immediately reconcile the two reports.

More efficient centrifuges

Iran has a major uranium enrichment facility in Natanz in central Iran where nearly 8,000 centrifuges are operating. Tehran began enrichment at Natanz in April 2006.

The Fordo centrifuges however are reportedly more efficient, and the site better shielded from aerial attack.

In this Sept. 26, 2009 file, satellite image provided by GeoEye shows a facility under construction inside a mountain located about 32 kilometres north northeast of Qom, Iran. (Associated Press/GeoEye Satellite Image, IHS Jane's Analysis, File)

Meanwhile, Khorasan daily quoted Revolutionary Guard deputy commander Ali Ashraf Nouri as saying that a strategic decision to close the Strait of Hormuz, should Iran's exports be blocked, has been made by Iran's top authorities.

"The supreme authorities ... have insisted that if enemies block the export of our oil, we won't allow a drop of oil to pass through the Strait of Hormuz. This is the strategy of the Islamic Republic in countering such threats," Nouri was quoted by Khorasan daily as saying.

One-sixth of the world's oil flows to market through the Strait of Hormuz, at the mouth of the Persian Gulf.

Iranian politicians have issued similar threats in the past, but this is the strongest statement yet by a top commander in the country's security establishment indicating that a closure of the strait is official policy.

The U.S. has recently enacted new sanctions targeting Iran's central bank and its ability to sell petroleum abroad, as part of its reponse to Tehran's nuclear program.