WASHINGTON (CNN)  -- The Obama administration is working on a substantial sanctions package against Iran in case current diplomatic efforts to curb its nuclear program fail, top officials told Congress on Tuesday.



Treasury Under Secretary Stuart Levy also developed some of the existing financial sanctions against Iran.



Under Secretary of the Treasury Stuart Levy, who developed some of the existing financial sanctions against Iran under the Bush administration, said at a Senate Banking Committee hearing that the "comprehensive" plan would target "key vulnerabilities and fissures" in Iran to show Tehran that it would face "serious costs" for thwarting international demands.



"It takes into account that no single sanction is a 'silver bullet'; we will need to impose measures simultaneously in many different forms in order to be effective," Levy said.



He stressed, however, that the United States would be mindful of actions that would harm the Iranian people or undercut the opposition battling the Iranian government.



The hearing comes as some members of Congress push for tougher U.S. sanctions on the Iranian regime in light of the recent revelation that Iran was building a second uranium enrichment facility near Qom, a dramatic development that jacked up tension between Iran and international powers.



During talks last week in Geneva, Switzerland, between Iranian officials and representatives of the so-called P5+1 -- the United States, Britain, France, German, Russia and China -- Iran agreed to admit inspectors from the International Atomic Energy Agency to the Qom facility.



Tehran also agreed "in principle" to ship its low-enriched uranium produced in Iran to third countries for further enrichment for a nuclear reactor used for medical research.



Deputy Secretary of State James Steinberg told the panel Tuesday that one reason for the Obama administration's engagement toward Iran was to secure international support for sanctions if Iran continued to defy international demands. Last week's talks, he said, shined a "spotlight" on Iran that makes inaction more costly.



Levy also stressed that an international coalition was key to keeping pressure on Iran.



"Because financial measures are most effective when imposed as part of a broad-based effort with support of the largest possible international coalition, we are working closely with our allies as we put together this strategy," he said. "The less united we are in applying pressure, the greater the risk our measures will not have the impact we seek."



Several lawmakers expressed doubt that Iran would negotiate in good faith and threatened legislation to impose tough new sanctions against Tehran.



Committee Chairman Christopher Dodd, D-Connecticut, said he planned to move forward this month on a proposal to expand financial restrictions, impose new sanctions on Iran's oil and gas sectors and ban both the export of refined gasoline products to Iran and the import of Iranian goods.



Steinberg said the United States and its allies will judge Iran's seriousness about the talks by whether it makes good on its commitments to ship the uranium out of the country and admit the IAEA inspectors, who are expected to visit the Qom facility October 25.



"By the end of the month, we will have some very clear indications of what their intentions are," he said.
What is key to keeping pressure up? Who could possibly be harmed? What would target "key vulnerabilities,"? What would the U.S. be mindful of? Who would be mindful of actions that would harm Iranian people? What is the key to keeping the pressure up?
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question: What is key to keeping pressure up?, answer: international coalition | question: Who could possibly be harmed?, answer: Iranian people | question: What would target "key vulnerabilities,"?, answer: "comprehensive" plan | question: What would the U.S. be mindful of?, answer: harm the Iranian people or undercut the opposition | question: Who would be mindful of actions that would harm Iranian people?, answer: United States | question: What is the key to keeping the pressure up?, answer: Levy also stressed that an international coalition was