In making the offer earlier in the day, Israel said the window would not apply to areas in which Israeli soldiers were already operating, and Israel would "respond to any attempt to exploit this window to harm" civilians or troops. It also told residents to stay away from areas they've been asked to evacuate.
Fighting raged in many areas of Gaza, with Israel reporting militants hit, soldiers wounded, and 40 "terror activity sites" struck.
Israeli soldiers killed
Three more Israeli soldiers were killed Wednesday, bringing the total to 56 dead since Operation Protective Edge began July 8. Three civilians also have been killed in Israel.
The Israel Defense Forces said the soldiers were uncovering a tunnel shaft in a home in southern Gaza. "The house and the tunnel were booby trapped with two explosive devices that were detonated," the IDF said.
Hamas said its fighters "lured a special Zionist unit which consisted of between 15 to 20 soldiers to a booby-trapped house with 12 IED canisters."
Twenty-seven Israeli soldiers were wounded in several incidents Wednesday in Gaza, the IDF said.
Shelling near a market
Hamas TV said many people were killed in shelling near a street market in northern Gaza. The Gaza Health Ministry reported 17 killed.
Israel has said errant Hamas rocket fire is responsible for some of the attacks in Gaza.
More than 1,300 Palestinians have been killed since the conflict between Israel and Hamas began this month, the Palestinian Ministry of Health in Gaza said.
The number of militants killed is unclear, but the United Nations estimates that 70% to 80% of the dead are civilians.
U.N. facility struck
The United Nations condemned Israel for attacking a school Wednesday that was being used as a shelter for 3,000 Palestinians.
U.N. spokesman Chris Gunness said his group's initial assessment indicates Israeli artillery hit the school. The number of deaths was not immediately clear, Gunness said. The Palestinian Health Ministry said 20 were killed.
But Israel said a group of militants fired at Israeli soldiers from the vicinity, and the soldiers "responded by firing at the origin of the fire," a military spokesman said.
"If our forces were involved in a firefight, it's because Hamas has decided that it's open season on the U.N.," Israeli government spokesman Mark Regev told CNN Wednesday.
Israel has said a Hamas misfire was responsible for a previous attack on a U.N. facility.
"More than 200 rockets fired from Gaza have hit Gaza since July 8. Palestinian terrorists fire from civilian areas and hit their own people," the IDF said on Twitter, along with videos that the military said show Hamas fighters launching attacks from inside homes, mosques, hospitals and schools.
Rockets have been found inside U.N. facilities in Gaza. The latest such discovery was Tuesday, the United Nations said.
"We condemn the group or groups who endangered civilians by placing these munitions in our school," Gunness said.
After the school was struck Wednesday, Gunness said, "We have moved beyond the humanitarian realm. We are overwhelmed. ... There are tens of thousands of people in the streets in Gaza without food, without water, without shelter. That's why we call on the international community to take deliberate political action to end this ongoing carnage."
More than 200,000 Palestinians are packing into 85 shelters across Gaza, Gunness said Wednesday, calling the situation a "human displacement crisis."
U.N. official: 'The world stands disgraced'
Pierre Krahenbuhl, head of the U.N. agency for Palestinians, insisted the school was hit by Israeli shelling.
"Children killed in their sleep; this is an affront to all of us, a source of universal shame," Krahenbuhl said in a statement. "Today the world stands disgraced."
A strike Tuesday severely damaged Gaza's only power plant. Israel said it did not target the plant, and that a Hamas rocket may have been to blame.
Either way, residents must depend almost entirely on small generators for electricity. Clean water is inaccessible for most. And some 3,600 people have lost their homes.
"We cannot supply electricity" for hospitals, sewage treatment or domestic use, said Fathi al-Sheikh Khalil, deputy chairman of the Palestinian Energy Natural Resources Authority in Gaza. "This is a disaster."
Israel delivers some fuel
The Israeli Foreign Ministry, meanwhile, announced on Twitter that Israel has sent into Gaza more than 4 million liters of diesel for the power station, 3 million liters of fuel and 800,000 liters of benzene for transportation, and 1.6 tons of gas for domestic use during the conflict.
In the wake of the power plant being hit, the Coordination of Government Activities in the Territories "is working with Israeli civilian and military officials, international organizations and Palestinian representatives to try and find immediate solutions," the ministry said.
Forty-three trucks "carrying over 750 tons of food, medicine & supplies" entered Gaza Wednesday from Israel, the ministry said. It provided information on how people can donate humanitarian supplies, and a contact at the Palestinian Customs Agency.
Some Palestinians have been brought into Israel from Gaza for medical care, the ministry said.
U.S. resupplies Israeli ammo
The United States, meanwhile, agreed to Israel's request to resupply it with several types of ammunition.
It's not an emergency sale, a U.S. defense official told CNN.
Among the items being bought are 120mm mortar rounds and 40mm ammunition for grenade launchers, officials said. Those will come from a stockpile the United States keeps in Israel, which is worth more than $1 billion.
Nations pull ambassadors
Chile, Peru, Brazil and Ecuador have pulled their ambassadors out of Tel Aviv to protest the Israeli offensive.
Regev called that "incomprehensible." Israel is democratic, peaceful, and "acting to protect its citizens," he said.
"On the other side you have a brutal terrorist organization, Hamas, which is committed to the destruction of Israel; that says every Israeli civilian is a legitimate target in its war of terror, that says the only solution to the conflict is the elimination of my country, violent jihad. And they are shooting rockets at the Israeli civilian population. And at the same time they are adopting tactics, turning Gaza citizens into human shields, deliberately endangering them."
Polls: Israelis don't want cease-fire, Palestinians don't want two-state solution
While the vast majority of casualties are Palestinians in Gaza, Israel continues to ward off rocket attacks from Gaza with its Iron Dome missile defense system. Israeli officials say they are committed to destroying tunnels used by Palestinian militants in Gaza to make their way into Israel.
A poll released this week showed 86.5% of Jewish Israelis surveyed say Israel cannot accept a cease-fire because "Hamas continues firing missiles on Israel, not all the tunnels have been found, and Hamas has not surrendered," according to the Jerusalem Post.
It's unclear how many in Gaza want militants to stop rocket attacks.
Last month, a poll by the Washington Institute for Near East policy found most Palestinians in Gaza oppose a two-state solution and want to work toward a five-year goal of abolishing Israel. But the majority said they support nonviolent methods of "popular resistance."
Most Israelis support a two-state solution, according to a poll by the Dialog Institute, Haaretz reported.