Israel prepared Thursday for a possible ground invasion in the Gaza Strip as Palestinians, who spent the night in pitch darkness amid the ruins of pulverized neighborhoods, continued to be denied access to vital humanitarian aid.

International aid groups warned that deaths in Gaza could accelerate as Israel prevents delivery of supplies. The conflict, ignited by a Hamas incursion into Israel, has already claimed at least 2,400 lives on both sides.

Lt. Col. Richard Hecht, an Israeli military spokesman, told reporters Thursday that forces "are preparing for a ground maneuver if decided," but that the political leadership has not yet ordered one.

A ground offensive in Gaza, the first since the 2014 war, would likely bring even higher casualties on both sides in brutal house-to-house fighting.

In Gaza, Palestinians fleeing airstrikes can be seen running through the streets, carrying their belongings and looking for a safe place. Hundreds of thousands have crowded into U.N.-run schools while others are staying with relatives or even strangers who let them in.

Lines form outside bakeries and grocery stores during the few hours they dare to open, and the bakeries could soon shut down for lack of fuel or power.

Israeli Prime Minister Benjamin Netanyahu vowed to "crush and destroy" Hamas with the support of a new war cabinet formed Wednesday that includes a longtime opposition critic.

The U.S. has pledged unwavering support for Israel's response, and Secretary of State Antony Blinken arrived in Tel Aviv on Thursday to meet with Netanyahu and other Israeli leaders.

The Israeli military said overnight strikes once again targeted Hamas infrastructure while another airstrike killed a commander with the Islamic Jihad in his family home in the northern town of Beit Lahia, according to local media.

The Hamas-run Interior Ministry said Israeli strikes demolished two multi-story houses on top of residents without warning, killing and wounding "a large number" of people, mainly civilians.

Israel has halted the entry of food, water, fuel and medicine into the territory. On Tuesday, Gaza's only power station ran out of fuel and shut down, leaving only lights powered by scattered private generators. Those will shut off as well if fuel is not allowed in.

A senior official with the the International Committee of the Red Cross warned that lack of electricity could cripple hospitals.

"As Gaza loses power, hospitals lose power, putting newborns in incubators and elderly patients on oxygen at risk. Kidney dialysis stops, and X-rays can't be taken," said Fabrizio Carboni, ICRC's regional director. "Without electricity, hospitals risk turning into morgues."

In Israel, opposition leader Benny Gantz, a former defense minister and political opponent of Netanyahu, joined a new wartime cabinet. Israel has mobilized 360,000 reservists, massed additional forces near Gaza and evacuated tens of thousands of residents from nearby communities.

The Israeli government is under intense public pressure to topple Hamas after its members stormed through a border fence Saturday.

Netanyahu has alleged that the attackers engaged in atrocities, which could not be independently confirmed, and authorities did not immediately offer further details. Rescue workers and witnesses, however, have described finding bodies of civilians and soldiers.

Hamas, in the meantime, are holding an estimated 150 people taken hostage from Israel, both combatant and non-combatant.

Israel's increasingly destructive airstrikes in Gaza have flattened entire city blocks and left unknown numbers of bodies beneath debris. A ground offensive in Gaza, whose 2.3 million residents are densely packed into a strip of land only 40 kilometers (25 miles) long, would likely result in a surge of casualties on both sides.

The U.N. said late Wednesday the number of people displaced by the airstrikes had soared 30% within 24 hours, to 339,000, two-thirds of them crowding into U.N. schools. Others sought shelter in the shrinking number of safe neighborhoods.

The Egyptian government rejected an American proposal to allow Palestinians fleeing Israel's bombardment to leave Gaza, a senior Egyptian official said early Thursday, speaking on condition of anonymity because he was not authorized to talk to the press.

Egypt believes that Palestinians leaving Gaza would harm the Palestinian cause, and its state-run media reported that the Israeli offensive is part of a scheme to empty the enclave.

Convoys stood loaded with fuel and food Wednesday on the Egyptian side of the Rafah crossing, but were unable to enter Gaza, the official said. The only crossing point between Egypt and Gaza was shut down Tuesday following nearby Israeli airstrikes.

The official said Egypt was talking with Israel and the U.S. on establishing safe corridors inside Gaza and delivering humanitarian aid to the besieged Palestinians, and with Israel and other foreign governments to evacuate foreigners through the Rafah crossing point.

The risk of the war spreading was evident Wednesday after the Iranian-backed Lebanese group Hezbollah fired anti-tank missiles at an Israeli military position and claimed to have killed and wounded troops.

The Israeli military confirmed the attack but did not comment on possible casualties. The Israeli army shelled the area in southern Lebanon where the attack was launched.

The death toll in Gaza rose to 1,200 early Thursday, the Palestinian health ministry said.

The Gaza Strip's biggest hospital, Al-Shifa, has only enough fuel to keep power on for three days, said Matthias Kannes, a Gaza-based official for Doctors Without Borders. The group said the two hospitals it runs in Gaza were running out of surgical equipment, antibiotics, fuel and other supplies.

Ghassan Abu Sitta, a reconstructive surgeon at al-Shifa, said he had 50 patients waiting to go to the operating room.

"We're already beyond the capacity of the system to cope," he said. The health system "has the rest of the week before it collapses, not just because of the diesel. All supplies are running short."

The Palestinian Red Crescent said other hospitals' generators will run out in five days. Residential buildings, unable to store as much diesel, likely will go dark sooner.

In the West Bank, Israeli settlers attacked a village south of Nablus, opening fire on Palestinians and killing three, the territory's Health Ministry said. More than two dozen Palestinians have died in fighting in the West Bank since the weekend.

In a new tactic, Israel is warning civilians to evacuate whole Gaza neighborhoods, rather than just individual buildings, then leveling large swaths in waves of airstrikes.

Israel's tone has changed as well. In past conflicts, its military insisted on the precision of strikes in Gaza, trying to ward off criticism over civilian deaths. This time, military briefings emphasize the destruction being wreaked.

Even with the evacuation warnings, Palestinians say some are unable to escape or have nowhere to go, and that entire families have been crushed under rubble.

Other times, strikes come with no notice, survivors say.

"There was no warning or anything," said Hashem Abu Manea, 58, who lost his 15-year-old daughter, Joanna, when a strike late Tuesday leveled his home in Gaza City.

The Israeli military said more than 1,200 people, including 189 soldiers, have been killed in Israel, a staggering toll unseen since the 1973 war with Egypt and Syria that lasted weeks.

Israel says roughly 1,500 Hamas members were killed inside Israel, and that hundreds of the dead inside Gaza are Hamas members.