JERUSALEM – Facing warnings of a looming humanitarian crisis in the Gaza Strip, Israel on Sunday allowed food shipments through the main cargo crossing to the territory and restored fuel supplies cut off after the abduction of an Israeli soldier.

Israeli artillery batteries and naval boats shelled the coastal strip for the fifth straight day and warplanes struck a target in Gaza City early today, keeping up the pressure to release the captive soldier, Cpl. Gilad Shalit, 19, who was seized June 25 in an attack on an Israeli outpost by Palestinian militants from Hamas and two other groups.

Since an Israeli offensive began Wednesday, more than 1,500 shells have been fired at open areas in the northern and southern Gaza Strip, according to army and U.N. statistics. The shell explosions, along with sonic booms set off at night by Israeli planes, have heightened anxiety in Palestinian households, especially among children, residents said. The Israeli moves to allow in vital supplies came after United Nations officials and the Red Cross said they were concerned about deteriorating conditions in Gaza in the wake of Israeli airstrikes last week that knocked out power to wide areas and destroyed bridges and roads.

Secretary of State Condoleezza Rice voiced similar concerns in a telephone conversation Sunday with Israeli Prime Minister Ehud Olmert, who replied that there was no humanitarian crisis in Gaza and that Israel had allowed supplies into the area, his office said.

More than 50 trucks carrying milk, meat, wheat, flour, cooking oil, fruit and other staples moved into the Gaza Strip through the Karni Crossing, and diesel fuel, gasoline and natural gas were transferred through pipelines at a terminal in Nahal Oz, army officials said. Israel had shut the crossing and stopped supplying fuel after the attack on the border outpost.

The destruction of Gaza’s only power plant in an Israeli airstrike Wednesday knocked out 43 percent of the electricity furnished to the territory, leading to increased demand for diesel fuel to run generators to power hospitals and water pumping stations. Gas stations were also running out of fuel by the weekend.

Power routinely supplied by Israel to parts of the Gaza Strip is now being distributed intermittently throughout the territory for periods of six hours, according to local residents. The army said Israel had increased the electricity and water it provides the territory.

Palestinians have accused Israel of worsening conditions for ordinary Gazans in an effort to turn them against the Hamas-led government and create public pressure for the release of the captive soldier.

Olmert insisted Sunday that the Israel “is not interested in harming the Palestinian population.”

But Interior Minister Roni Bar-On, a close ally of Olmert, said civilian hardship was part of the prime minister’s plan.

“The prime minister explicitly directed the army that no one should sleep at night in Gaza – explicitly, that there should be discomfort there,” Bar-On told Israel Radio. “The equation is very clear: If people won’t live at peace here, they won’t live at peace in Gaza.”

Early Monday, Israeli aircraft struck a building in Gaza City the army said was used as an operations center by Al-Aqsa Martyrs’ Brigades, a militant group linked to the Fatah party of Palestinian President Mahmoud Abbas.

The attack came nearly 24 hours after Israeli aircraft rocketed the empty office of Palestinian Prime Minister Ismail Haniyeh of Hamas. Abbas joined Haniyeh in inspecting the damage and condemned what he called “the destruction of the civilian institutions of the Palestinian people.”

A spokesman for the armed wing of Hamas threatened to attack targets in Israel similar to those struck by Israel in Gaza.

The continuing military action came as Egyptian mediators tried to broker a deal for the release of the soldier, with no apparent signs of progress. The Egyptians were reportedly working on a proposal that the soldier would be freed in exchange for an Egyptian commitment that Israel would release prisoners at an unspecified later date.

The armed wing of Hamas and two allied groups holding the soldier, the Popular Resistance Committees and the Army of Islam, have demanded the release of 1,000 Palestinian and other Arab prisoners held in Israeli jails, the freeing of an additional 500 imprisoned women and minors, and a halt to the Israeli offensive.

However, Israel, which has exchanged Arab prisoners for captured servicemen in the past, rejected any prisoner swap.

“These are not easy days for the State of Israel, but we have no intention of surrendering to blackmail,” Olmert said Sunday at the start of the weekly Cabinet meeting. “Everyone knows that surrendering to terrorism today means inviting the next act of terrorism.”

Abbas’ office said in a statement Saturday that negotiations were being hampered by “the absence of an address on the Hamas side,” and that Khaled Mashaal, the overall leader of Hamas, who is based in Syria, was passing responsibility to the Hamas armed wing in Gaza while the armed wing was saying decisions rested with Mashaal.

As diplomatic efforts ran into complications, Israel kept forces ready for a push into the northern Gaza Strip, where militants have launched crude rockets into southern Israel.

Last week tanks and troops entered the southern Gaza Strip, where the captive soldier is believed to be held, taking over an unused airport near the border town of Rafah. Troops there killed three militants Sunday night, two of whom were wearing explosive belts, the army said.

Israel also increased pressure on Hamas by arresting dozens of its political leaders in the West Bank last week, including 8 Palestinian Cabinet ministers and more than 20 legislators.

Israeli officials said the Hamas members were being held on suspicion of involvement in terrorist activity. But Zehava Galon, an Israeli lawmaker from the leftist Meretz party, asserted that the Hamas officials were being held “on dubious legal grounds” as bargaining chips for the release of the soldier.

“A state can’t act like a gang,” Galon said. “A state cannot kidnap.”

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