Three days after Defense Minister Ehud Barak ordered the Gaza Strip sealed off to the outside world, defense officials said Sunday that food supplies were running low in Gaza and would dry up by the middle of the week. The Palestinians were also facing a major shortage in medicine and medical supplies, the officials said. By Sunday night, only four Kassam rockets had been fired into Israel, a significant drop in comparison to the more than 160 that pounded the western Negev last week. Despite the dwindling supplies, however, officials said Gaza was not facing a humanitarian crisis. "We will not allow a humanitarian crisis to develop there," a senior defense official said. "In the meantime, if the Palestinians want food or medicine, they can turn to Egypt and start to take care of themselves." On Sunday, 43 patients and their companions were allowed to cross into Israel for medical treatment. Large parts of the Gaza Strip were plunged into darkness Sunday night after the local electrical plant closed down completely due to fuel shortage. The Palestinian Energy Authority had begun shutting the plant's turbines early in the morning. Plant director Rafik Maliha said the regular fuel delivery from Israel had not arrived because the Nahal Oz terminal had been closed since Thursday. He said power outages would affect hospitals, sewage works and refrigerators, as well as water-purifying systems. Gaza Energy Authority head Kanan Obeid called on people to cut back their use of electrical appliances. The UN organization in charge of Palestinian refugees, UNRWA, warned that the Israeli blockade would drastically affect hospitals, sewage treatment plants and water facilities. "The logic of this defies basic humanitarian standards," said UNRWA spokesman Christopher Gunness. Human rights groups also condemned the fuel cutoff. The British group Oxfam called it "ineffective as well as unlawful." Gisha, an Israeli group that has fought the fuel cutbacks in the Supreme Court, said that "punishing Gaza's 1.5 million civilians does not stop the rocket fire; it only creates an impossible 'balance' of human suffering on both sides of the border." Defense officials, however, dismissed Palestinian claims of a complete blackout in Gaza, saying that 70 percent of the electricity Israel supplied to Gaza was still flowing into the Palestinian territory. "The claim that there is a complete blackout in Gaza is a spin," an official said, adding that the Palestinians had had enough fuel for the electrical plant to last at least a week before Barak's decision to shut down the crossings on Thursday night. Palestinian Authority officials in Ramallah expressed hope that the looming humanitarian crisis in the Gaza Strip would prompt Palestinians to turn against the Hamas government. "We hope the residents of the Gaza Strip will now realize that Hamas has only brought disaster upon them," a senior PA official told The Jerusalem Post. "The only way to resolve the crisis is by getting rid of Hamas." Another PA official said Hamas was also responsible for the fuel shortage. "Hamas has been stealing much of the fuel coming into the Gaza Strip," he charged. "They have enough fuel to fill their cars and keep the homes of their leaders heated." Hamas dismissed the allegations, accusing PA President Mahmoud Abbas and his Fatah party of "colluding" with Israel to overthrow the Hamas government. Hamas spokesman Sami Abu Zuhri said the latest pressure was aimed at forcing Hamas and the Palestinians to succumb. "The Zionist crimes against our people mean that we have all been sentenced to death," he said. "The world is watching as the Palestinians are dying slowly." He said the Gaza Strip was now "living in the Middle Ages" because most families did not have electricity. "Despite the pressure, we will never surrender," he added. "The international community is responsible for the catastrophe." AP contributed to this report.