Iran has already begun enriching uranium at a new underground site heavily protected from possible air strikes, according to a newspaper identified with the country's clerical leadership.
If true, yesterday's claims that enrichment has already started at the Fordo facility "amid heightened foreign enemy threats" will add to the tensions with Western governments promising further sanctions to forestall Iran's progress to becoming a nuclear power.
They came as Iran reportedly staged military exercises in eastern Iran, in what appeared to be a show of military resolve directed at US forces in Afghanistan.
The Kayhan newspaper, whose manager is a representative of Iran's Supreme Leader Ayatollah Ali Khamenei, reported the regime had begun injecting uranium gas into sophisticated centrifuges at the Fordo facility, some 20 miles from Qom.
Iran only acknowledged the existence of the Fordo site, buried 300 feet under rock, and defended by the Revolutionary Guard and ground-to-air missile batteries, after Western intelligence agencies identified it in September 2009.
The site, next to a military base, is reportedly both more efficient and better protected from aerial attack than the big Natanz uranium facility, which began operating in April 2006.
Yesterday's report came less than 24 hours after a declaration by the head of Iran's nuclear programme, Fereidoun Abbasi, that Tehran would "soon" begin enrichment at Fordo.
Tehran continues to insist that it is only developing nuclear power for energy and medical research, and has refused UN-backed calls to halt uranium enrichment. The US and Israel have both said that all options remain open, including military action, if the enrichment programme continues.
US President Barack Obama approved new sanctions against Iran a week ago, aimed at its central bank and at curbing its ability to sell petroleum abroad – but with a delay of six months because of fears of the impact of an oil price rise on the struggling world economy.
This has already prompted a series of threats by Tehran to close the strategic oil route through the Strait of Hormuz if the country's petroleum exports are blocked. These intensified yesterday with another newspaper report quoting a senior commander of the Revolutionary Guard, Al Ashraf Nouri, as saying: "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."
He was quoted by the Khorasan newspaper as adding: "The exalted leader [Ayatollah Khamenei] determined a new strategy for the armed forces, by which any threat from enemies will be responded to with threats." One-sixth of the world's oil flows through the Strait.