The Obama administration zeroed in on Iran's all-powerful Revolutionary Guard by imposing new sanctions Wednesday on the force behind suspect nuclear work and urging the world to do the same.
It ordered a freeze on assets of an individual and four firms linked to the Revolutionary Guard -- a unilateral US step toward what President Barack Obama has warned will be a "significant regime of sanctions" backed internationally.
The Treasury Department designated a Revolutionary Guard commander and four subsidiaries of a construction firm owned or controlled by the elite unit as "proliferators of weapons of mass destruction and their supporters."
State Department spokesman Philip Crowley said the US is targeting the Islamic Revolutionary Guard Corps for its role in Iran's nuclear and missile programs, alleged links to terrorism and crackdown on anti-government protests.
The Revolutionary Guard, which has been hit by repeated sanctions in the past, is also a major business force in Iran.
Crowley said US diplomats put "particular emphasis" on the elite military branch when they consult with other powers about sanctions, but they were not yet ready to offer a draft resolution to the UN Security Council.
"Our objective here is to try to put pressure on the government and those who are supporting its policies, without having undue impact on the Iranian people," Crowley told AFP.
The United States has been consulting with Russia, China, Britain, France and Germany on Iran, but Beijing wants a negotiated solution and now appears to be the lone hold-out against sanctions.
All but Germany are veto-wielding members of the UN Security Council.
The six powers have been leading a multi-year effort to curb Iran's uranium enrichment program, which the West fears masks a drive to build a nuclear bomb. Iran denies the charge, saying it is for peaceful use of energy.
The Obama administration has stepped up the pressure since Iran announced on Tuesday that it had begun work to enrich uranium to 20 percent, which it says is for a medical research reactor in Tehran.
The move suggested Iran was spurning a four-month-old proposal by the UN's International Atomic Energy Agency (IAEA) to ship most of its stocks of 3.5-percent enriched uranium abroad to be further upgraded to fuel the reactor.
Experts say that once Iran enriches uranium to 20 percent, it can proceed to the 93 percent needed to produce nuclear weapons since the technology is the same. Iran maintains the enrichment is purely for civilian energy purposes.
After trying to engage Iranian leaders and persuade them to accept the IAEA deal to defuse the crisis, Obama said the world must be prepared to pressure Iran to change course, even if the "door is still open" to negotiations.
A US official, speaking to AFP on condition of anonymity, said that the Revolutionary Guard is allowed to benefit from big non-bid government contracts that normal Iranian companies have no capacity to seek.
In previous years the guard corps might "have been able to profit from sanctions through their black market activities, but now they're so embedded in the economy that they can be targeted," the official said.
Indeed, the Guards now permeate all areas of Iran, with their engineering arm picking up massive contracts and former cadres, like ex-commander Mohsen Rezai who has stood twice for the presidency, moving into politics.
In business, the Guards now reap an increasingly substantial income which the United States is seeking to block.
Crowley neither confirmed nor denied reports that the administration was looking at possibly expanding the number of Iranians denied visas and placing curbs on energy sectory investments.
"We're looking at a range of options, and obviously the energy sector is a potential option," Crowley said. "But as to the specific steps we'll take, we're not prepared to discuss those publicly."
Iranian users meanwhile are having trouble accessing Gmail, Google said Wednesday following a report that Iran's telecommunications agency had permanently suspended the Internet giant's email service.
The reported move comes on the eve of street marches in Iran marking the 31st anniversary of the Islamic revolution and opposition plans to hold anti-government demonstrations.
