The foreign minister of Egypt, a key mediator in the conflict, accused Israel of using "starvation as a weapon" in "a flagrant and clear violation of humanitarian law." Saudi Arabia called Israel's decision "a tool of extortion."
Hamas accused Israel of trying to derail the ceasefire hours after its first phase had ended and called Israel's decision to cut off aid "a war crime and a blatant attack" on a truce that took a year of negotiations before taking hold in January.
The first phase saw a surge in humanitarian aid after months of growing hunger. It expired on Saturday. In the second phase, Hamas could release dozens of remaining hostages in return for an Israeli pullout from Gaza and a lasting ceasefire. Negotiations on the second phase were meant to start a month ago but haven't begun.
Israel said Sunday that a new U.S. proposal calls for extending the ceasefire's first phase through Ramadan - the Muslim holy month that began over the weekend - and the Jewish Passover holiday, which ends on April 20.
Under that proposal, Hamas would release half the hostages on the first day and the rest when an agreement is reached on a permanent ceasefire, Israeli Prime Minister Benjamin Netanyahu said. The militants currently hold 59 hostages, 35 of them believed to be dead.
Saying the ceasefire has saved countless lives, the International Committee of the Red Cross said that "any unraveling of the forward momentum created over the last six weeks risks plunging people back into despair."
U.N. humanitarian chief Tom Fletcher called Israel's decision "alarming," noting that international humanitarian law makes clear that aid access must be allowed. Medical charity MSF accused Israel of using aid as a bargaining chip, calling that "unacceptable" and "outrageous."
Five non-governmental groups asked Israel's Supreme Court for an interim order barring the state from preventing aid from entering Gaza, claiming the move violates Israel's obligations under international law: "These obligations cannot be condition on political considerations."
The U.S. had no immediate comment, and it wasn't clear when U.S. envoy Steve Witkoff, who was expected to visit the region last week, would arrive.
Netanyahu said Israel is fully coordinated with the Trump administration and the ceasefire will only continue as long as Hamas keeps releasing hostages.
The war has left most of Gaza's population of over 2 million dependent on international aid. About 600 aid trucks had entered daily since the ceasefire began on Jan. 19, easing fears of famine raised by international experts.
But residents said prices shot up as word of the closure spread.
From the heavily destroyed Jabaliya urban refugee camp, Fayza Nassar said the closure would worsen dire conditions.
"There will be famine and chaos," she said.
Hamas warned that any attempt to delay or cancel the ceasefire agreement would have "humanitarian consequences" for the hostages. The only way to free them is through the existing deal, the group said.
Israel was accused of blocking aid throughout the war
Israel imposed a siege on Gaza in the war's opening days and only eased it under U.S. pressure. U.N. agencies and aid groups accused Israel of not facilitating enough aid during 15 months of war.
The International Criminal Court said there was reason to believe Israel had used "starvation as a method of warfare" when it issued an arrest warrant for Netanyahu last year. The allegation is also central to South Africa's case at the International Court of Justice accusing Israel of genocide.
Israel has denied the accusations. It says it has allowed in enough aid and blamed shortages on what it called the U.N.'s inability to distribute it. It also accused Hamas of siphoning off aid.
Kenneth Roth, former head of Human Rights Watch, said Israel as an occupying power has an "absolute duty" to facilitate humanitarian aid under the Geneva Conventions, and called Israel's decision "a resumption of the war-crime starvation strategy" that led to the ICC warrant.
The war began when Hamas-led militants stormed into southern Israel on Oct. 7, 2023, killing some 1,200 people, mostly civilians, and taking 251 hostage.
Israel's offensive has killed over 48,000 Palestinians, according to Gaza's Health Ministry. It says more than half of those killed were women and children. It does not specify how many of the dead were combatants.
Israeli bombardment pounded large areas of Gaza to rubble and displaced some 90% of the population.
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This story has been corrected to show that 35 of the remaining hostages are believed to be dead, not 32.
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Magdy reported from Cairo. Associated Press writers Ellen Knickmeyer in Washington and Josef Federman in Jerusalem contributed to this report.