The United States on Friday expressed concern about the deteriorating humanitarian situation in Gaza, but officials blamed Hamas for Palestinian suffering and said it was difficult for the Israeli military to avoid civilian casualties. Officials said they were continuing to press Israel to take measures to prevent harming civilians and defended the decision to abstain in Thursday's UN Security Council vote on a resolution calling for an immediate but lasting cease-fire. Secretary of State Condoleezza Rice had helped negotiate the resolution. Rice said Friday that she was pleased that Israel had responded to calls to open a humanitarian corridor into Gaza, where the United Nations and aid agencies say a full-blown crisis has developed. But, she said, "it is very difficult in a circumstance like Gaza, which is a very densely populated area," to protect civilians. "It's also an area in which Hamas participates in activities like human shields and using buildings that are not designated as military buildings to hide their fighters," she told reporters at the State Department. "So it's hard." At the White House, spokesman Scott Stanzel said the administration is "very concerned about the humanitarian situation in Gaza" but echoed Rice's comments on the difficulties Israel faces. "We want to see that situation improve," he said. "However, it is a difficult situation. It is a conflict area. And this situation will not improve until Hamas stops lobbing rockets into Israel." Rice and State Department spokesman Sean McCormack sought to explain the seeming incongruity between US support for the Security Council resolution calling for a cease-fire and its decision not to vote on it. Rice, who spent three days in New York conducting frantic diplomacy on what eventually became the resolution, said the vote was "premature" because details of Egyptian President Hosni Mubarak's cease-fire initiative that the document endorses have not yet been worked out. At the same time, the US did not want to use its veto to kill the resolution, she said. "The US abstention was principally because we believed that it would have been useful to have a little bit more time for the Mubarak initiative to mature," she said. "It was simply believed that this might have been a little premature." Meanwhile, McCormack faced a barrage of questions from reporters about the apparent inconsistency of the abstention in the face of his declarations: "We support the text of this resolution. We support the goals of this resolution. We support the objectives of this resolution." "Our hope, again, in a perfect world, was that that resolution would have been referring to more specific actions that had to have been agreed upon as part of the Mubarak initiative," McCormack said. "That wasn't the case."