US Vice President Richard Cheney said Sunday that Israel did not warn America before launching its ground invasion of Gaza, but he backed the rationale for expanding the operation. "They didn't seek clearance or approval from us, certainly," he said on CBS's Face the Nation. "To go after that terrorist organization [Hamas], I think they probably decided that an air campaign wasn't enough, that they had to go in on the ground if they were going to take down the sites from which the rockets had been launched against Israel," Cheney said. He added that he was told over a period of months by the Israelis that they didn't want to have to act in Gaza, but that if the rocketing didn't stop, "they felt they had no choice but to take action. And if they did, they would be very aggressive, in terms of trying to take down Hamas. And that's exactly what's happened." Cheney labeled Hamas "the enemy," and said if there were to be a cease-fire, "it's got to be a sustainable, durable proposition, and Hamas has to stop rocketing Israel. And I don't think you can have a viable cease-fire until they're prepared to do that." The State Department said it was working toward a cease-fire in the wake of the IDF ground incursion, but stressed that any such halt in fighting must not be one that Hamas could breach at will with rocket fire. "It is obvious that that cease-fire should take place as soon as possible, but we need a cease-fire that is durable, sustainable, and not time limited," State Department spokesman Sean McCormack said. He criticized Hamas for causing hardship for Gazans, adding, "The United States is deeply concerned about the humanitarian situation and the protection of innocents. In this vein, we have expressed our concerns to the Israeli government that any military action needs to be mindful of the potential consequences to civilians." A senior US defense official said on the day of the invasion that Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, was informed in general terms of the ground incursion and its objectives through normal Israeli defense channels. The official spoke on condition of anonymity because he was referring to confidential US-Israeli contacts Saturday. US President George W. Bush was also briefed Saturday afternoon on the situation in Gaza, with White House spokesman Gordon Johndroe describing American officials as being in "regular contact with the Israelis as well as officials from countries in the region and Europe." Johndroe would not address whether the US was warned before the new stage of the offensive began on Saturday, but he said, "Their ground action is part of their overall operation. We continue to make clear to them our concerns for civilians, as well as the humanitarian situation." Other US political leaders defended Israel on Sunday, telling the morning news programs that Jerusalem's actions were understandable. "I think what the Israelis are doing is very important," said Senate Majority Leader Harry Reid of Nevada. "I think this terrorist organization, Hamas, has got to be put away. They've got to come to their senses." And Senate Minority Leader Mitch McConnell of Kentucky told ABC's This Week, "Hamas is a terrorist organization. Imagine in this country if somebody from a neighboring country were lobbing shells at our population. We'd do exactly the same thing. I think the Israelis are doing the only thing they can possibly do to defend their population." AP contributed to this report.