UNITED NATIONS - United Nations officials implored Israel to reverse its decision Friday to seal all border crossings with the Gaza Strip, warning that the violence in the region and cutoff of crucial supplies for 1.4 million Palestinians was provoking a humanitarian crisis.

The Defense Ministry closed all border crossings with Gaza on Friday and prevented the delivery of a United Nations aid shipment. Only humanitarian cases given Defense Minister Ehud Barak's personal approval would be allowed through, the ministry said.

"If milk is low in Gaza, the minister will be asked to approve a milk shipment, and it will enter," a Defense Ministry spokesman said.

"Such action cuts off the population from much-needed fuel supplies used to pump water and generate electricity to homes and hospitals," UN Secretary-General Ban Ki-moon said. "If this situation endures, the closure will also cause further shortages of food, medical and relief items in the Gaza Strip."

Ban urged an immediate end to the violence engulfing Gaza and southern Israel, including Palestinian sniper and rocket attacks into Israel, and he called on Israel's defense forces to use "maximum restraint."

He said he had "deep concern that the hostilities taking place on the ground will undermine the hopes for peace" that have come out of November's U.S.-sponsored Mideast peace conference in Annapolis, Maryland.

The UN Relief and Works Agency, which distributes cooking oil, flour and sugar to hundreds of thousands of Gazans, said it had about two months worth of supplies in its warehouses. However, "Gazans need to supplement the basics with nutritious foods, such as fruit, vegetables and proteins, which have become expensive and hard to find," said UNRWA spokesman Christopher Gunness.

The International Committee of the Red Cross called on Israel and the Palestinians to respect international law and stop harming civilians. Christoph Harnisch, head of the organization's delegation to Israel and the Palestinian territories, said in a statement he was in daily contact with the Israel Defense Forces and Palestinian armed factions in an effort to persuade them to respect the civilian population.

Defense Ministry spokesman Shlomo Dror said Gazans had sufficient stocks of food so that no one would go hungry. "There is a government decision that there will not be a humanitarian crisis in Gaza," Dror said.

The deputy head of Israel's mission to the United Nations, Daniel Carmon, told Reuters Israel's actions were "what any responsible government would do when it is confronted as we are with this surge of violence and terrorism."

He gave no indication of when the closure would end.

Israel sealed the Gaza border crossings to cut the flow of supplies in an attempt to pressure Hamas to halt its rocket fire, which kept falling in southern Israel. The violence has surged since Tuesday when an Israeli ground and air offensive against rocket squads killed 19 Palestinians.

The Gaza death toll had risen to 36, including at least 10 civilians, by Saturday.

"It is a crisis already," said John Holmes, the UN undersecretary general for humanitarian affairs, who called it "unacceptable" and "morally unjustifiable" that Israel closed the border to a daily average of 120 trucks of food and humanitarian supplies entering Gaza from Israel.

"In Gaza, we're getting to a situation where virtually all of the population is dependent on international aid supplies," he said. "This violence is putting what is already an extremely worrying and fragile humanitarian situation into an even more dangerous context."

"The Israeli reaction is not justified by those rocket attacks, even though it's caused by those rocket attacks," said Holmes.

A the behest of Arab and Muslim countries, the UN Human Rights Council will hold an emergency session next Wednesday to examine Israel's new measures in Gaza, a UN source said.

"Gaza is completely shut down. This will only add to an already dire situation," said Christopher Gunness, spokesman for the United Nations Relief and Works Agency (UNRWA), whose aid shipment on Friday was blocked.

The decision to close the crossings came after Israel vowed to broaden its military campaign against Gaza militants who have fired more than 130 rockets and 80 mortars at southern Israel in the last three days.