Frustrated by Iran's continued defiance of demands to come clean on its nuclear program, the Obama administration is leaning toward imposing new sanctions, even if it must act alone.

Administration officials acknowledged growing concern that there may not be international consensus to expand the existing U.N. sanctions, despite Tehran's apparent rejection of a confidence-building measure proposed by the U.N.'s nuclear watchdog in hopes of making progress on the nuclear issue.

To that end, the administration is quietly supporting legislation in Congress that would give President Barack Obama a broad new array of authority to target Iran's energy sector by penalizing foreign firms that sell and ship refined petroleum products to Iran. The regime is heavily dependent on gasoline, kerosene and propane imports.

The legislation would also allow the administration to go after insurance and reinsurance concerns that cover oil tankers and their cargo. And the U.S. could also target companies that provide Iran with covert technology used to crack down on protesters and democracy advocates as it did during demonstrations this summer after a disputed national election.

U.S. officials took a neutral public stance on the legislation when it cleared two key congressional panels this week. They were anxious not to endanger ongoing negotiations between the International Atomic Energy Agency and Tehran over a deal that would see most of Iran's low enriched uranium shipped out of the country for reprocessing, handicapping its ability to use the uranium for weapons instead of energy.

Secretary of State Hillary Rodham Clinton said in an interview with CNN on Friday that the administration wants to let the negotiating process "play out."

But White House press secretary Robert Gibbs expressed limited patience with Iran. "The president's time is not unlimited," he said when asked whether it was time to pursue tougher sanctions.

And privately, officials said they welcomed approval of the bills by the House Foreign Affairs Committee on Wednesday and the Senate Banking, Housing and Urban Affairs Committee on Thursday.

The officials spoke on condition of anonymity to discuss internal administration planning.

"We have to be prepared to act and we are not going to let this drag out forever," said one administration official.

Officials stress that they do not want the administration to act alone and would far prefer to have any new sanctions be adopted by the U.N. Security Council. The U.N. body has already adopted three sets of penalties on Iran, which would kick in if Iran continues to stonewall offers to cease uranium enrichment in exchange for incentives.

But resistance to any further sanctions from Russia and China, longtime foes of such measures, complicates the path. Those two nations would likely block any international sanctions efforts despite recent statements from Russian President Dmitry Medvedev that new penalties may be "inevitable," the officials said.

Iran's state news agency said Friday that the country is insisting on simultaneously exchanging its low-enriched uranium for nuclear fuel produced overseas. That would undermines the basis of the U.N. plan for it to ship most of its supply for further enrichment in Russia and to be turned into fuel rods in France for use in a research reactor.

At the same time, the agency quoted an unidentified official as saying an Iranian response to the Western offer "did not contain a reply" to the plan but simply expressed Iran's "positive attitude" and willingness to hold talks on the proposal.

Gibbs and State Department spokesman Robert Wood said the administration was waiting for clarification of the Iranian position. "We're in constant contact with the IAEA to get that," Gibbs said.

"We're waiting for that clarification so that we can go forward," Wood said. "It's a good agreement, it's a confidence-building measure."