US Secretary of State Hillary Clinton said Wednesday that the US is laying the foundations for "crippling" sanctions against Iran should diplomacy fail. In her first appearance before the US House Foreign Affairs Committee, Clinton defended the Obama administration's efforts to engage Iran, saying that "by following the diplomatic path we are on, we gain credibility and influence with a number of nations who would have to participate in order to make the sanctions regime as tight and crippling as we would want it to be." At the same time, Clinton did not respond to a question by committee chairman Howard Berman asking what time frame she had in mind for Iran engagement. Israel has advocated for a short dialogue process with clear timelines, a position that Berman echoed Wednesday when he said that "such engagement can't be open-ended" because "Teheran continues to enrich uranium, and every day moves closer to the nuclear threshold." Iran on Wednesday appeared to respond to some of the American outreach, with the official Iranian news agency IRNA reporting that Iran welcomes a "constructive" dialogue with world powers over its nuclear program, but insisted that it would not halt its uranium enrichment activities. Clinton did not clarify Wednesday how the issue of the suspension of enrichment would be handled by the new US leadership, as the Bush administration had demanded that enrichment be halted before negotiations could take place. But she did say that the US was now participating in the international negotiations led by the permanent UN Security Council members and Germany, known as the P5+1. "After years during which the United States basically sat on the sidelines, we are now a full partner in the P5+1 talks." she said. At the same time she stressed that, "We're deploying new approaches to the threat posed by Iran, and we're doing so with our eyes wide open and with no illusions. We know the imperative of preventing Iran from obtaining nuclear weapons." She said that "in the event that our offers are either rejected or the process is inconclusive or unsuccessful," the US was "laying the groundwork for the kind of very tough â€¦ crippling sanctions that might be necessary." During her testimony, the secretary of state also declared that the US was unwilling to work with a Palestinian unity government with an unreformed Hamas. "We will not deal with nor in any way fund a Palestinian government that includes Hamas unless and until Hamas has renounced violence, recognized Israel, and agreed to follow the previous obligations of the Palestinian Authority," she said. Clinton added, however, that "we want to leave open the door that that can happen" so the US added a waiver for the funding to flow to a Palestinian unity government if those conditions are met. "We're not betting on it," she noted. She also brushed off appeals by Rep. Keith Ellison (D-Minnesota) that the US should pressure Israel to open up the border crossings into Gaza and allow more types of goods and aid to flow into the coastal strip. "The crossings are no longer completely closed. There are many items that are being transported through the crossings," she said. "The best way for us to help the people of Gaza is for Hamas to cease its rocket-fire on Israel, to abide by the Quartet principles, and the same principles that were adopted by the Arab peace initiative."