Israeli warplanes carried out airstrikes early Sunday near Gaza's largest hospital, which is packed with patients and tens of thousands of Palestinians seeking shelter, residents said.
Israel has said Gaza's militant Hamas rulers have a command post under the hospital, without providing much evidence.
The strikes came a day after Israeli Prime Minister Benjamin Netanyahu announced a second stage in Israel's war on Hamas, three weeks after Hamas launched a brutal incursion into Israel October 7.
Tanks and infantry pushed into Gaza over the weekend in what officials described as a widening ground offensive as Israel pounded the territory from air, land and sea.
The bombardment described by Gaza residents as the most intense of the war knocked out most communications in the territory late Friday, largely cutting off the besieged enclave's 2.3 million people from the world.
Communications were restored to many people in Gaza early Sunday, according to local telecoms companies, Internet-access advocacy group NetBlocks.org and confirmation on the ground.
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In a sign of growing chaos in Gaza, the UN agency for Palestinian refugees said thousands of people broke into its Gaza aid warehouses to take food and other basic survival items" like hygiene products. Thomas White, the agency's director in Gaza, said the break-in was a worrying sign that civil order is starting to break down."
The agency, known as UNRWA, provides basic services to hundreds of thousands of people in Gaza. Its schools across the territory have been transformed into packed shelters housing Palestinians displaced by the conflict.
Residents said the latest airstrikes destroyed most of the roads leading to Shifa Hospital in Gaza City, in the northern part of the besieged territory.
Israel says most residents have heeded its orders to flee to the south, but hundreds of thousands remain in the north, in part because Israel has also bombarded targets in so-called safe zones.
Tens of thousands are sheltering in Shifa, which is also packed with patients wounded in the strikes.
Reaching the hospital has become increasingly difficult, Mahmoud al-Sawah, who is sheltering in the hospital, said over the phone. It seems they want to cut off the area.
Another Gaza City resident, Abdallah Sayed, said the Israeli bombing over the past two days was the most violent and intense since the war started.
The Israeli military had no immediate comment when asked about reports of strikes near Shifa.
The army recently released computer-generated images showing what it said were Hamas installations in and around Shifa Hospital, as well as interrogations of captured Hamas fighters who might have been speaking under duress. Israel has made similar claims before, but has not substantiated them.
Little is known about Hamas' tunnels and other infrastructure, and the claims could not be independently verified.
Hamas' government dismissed the allegations as lies and said they were a precursor for striking this facility.
On Saturday, the Israeli military released grainy images showing tank columns moving slowly in open areas of Gaza, apparently near the border, and said warplanes had bombed dozens of Hamas tunnels and underground bunkers.
The escalation ratcheted up domestic pressure on Israel's government to secure the release of some 230 hostages seized in the October 7 rampage, when Hamas fighters from Gaza breached Israel's defenses and stormed into nearby towns, gunning down civilians and soldiers in a surprise attack.
Desperate family members met with Netanyahu on Saturday and expressed support for an exchange for Palestinian prisoners held in Israel.
Hamas' top leader in Gaza, Yehia Sinwar, said Palestinian militants are ready immediately to release all hostages if Israel releases all of the thousands of Palestinians held in its prisons. Rear Adm. Daniel Hagari, an Israeli military spokesman, dismissed the offer as psychological terror.
Netanyahu told the nationally televised news conference that Israel is determined to bring back all the hostages, and maintained that the expanding ground operation will help us in this mission.
He said he couldn't reveal everything that is being done due to the sensitivity and secrecy of the efforts.
This is the second stage of the war, whose objectives are clear: to destroy the military and governmental capabilities of Hamas and bring the hostages home, he said in his first time taking questions from journalists since the war began.
Netanyahu also acknowledged that the October 7 debacle, in which more than 1,400 people were killed, would need a thorough investigation, adding that everyone will have to answer questions, including me.
The Israeli military said it was gradually expanding its ground operations inside Gaza, while stopping short of calling it an all-out invasion. Casualties on both sides are expected to rise sharply as Israeli forces and Palestinian militants battle in dense residential areas.
We are proceeding with the stages of the war according to an organized plan, Hagari, the military spokesman, said. The comments hinted at a strategy of staged escalation, instead of a massive and overwhelming offensive.
Despite the Israeli offensive, Palestinian militants have continued firing rockets into Israel, with the constant sirens in southern Israel a reminder of the threat.
The Palestinian death toll in Gaza rose Saturday to just over 7,700 people since the war began, with 377 deaths reported since late Friday, according to the Gaza Health Ministry. Most of those killed have been women and minors, the ministry said.
An estimated 1,700 people remain trapped beneath the rubble, according to the Health Ministry, which has said it bases its estimates on distress calls it received.
Israel says its strikes target Hamas fighters and infrastructure and that the militants operate among civilians, putting them in danger.
More than 1.4 million people across Gaza have fled their homes, nearly half crowding into UN schools and shelters, following repeated warnings by the Israeli military that they would be in danger if they remained in northern Gaza. No one has been allowed out of the sealed-off territory, and Israel has allowed only a trickle of food and medical aid to enter from Egypt.
Gaza's sole power plant shut down shortly after the start of the war, and Israel has allowed no fuel to enter, saying Hamas would use it for military purposes.
Hospitals are struggling to keep emergency generators running to operate incubators and other life-saving equipment, and the UN agency for Palestinian refugees is also trying to keep water pumps and bakeries running to meet essential needs.
The conflict has threatened to ignite a wider war across the region, with Lebanon's militant Hezbollah trading fire with Israel along the border.
In recent days, both Israel and the US have struck targets in Syria that they say are linked to Iran, which backs Hamas, Hezbollah and other armed groups in the Middle East. The US said it was responding to attacks on American forces in Syria and Iraq.
Israeli forces have also traded fire with Palestinian militants in the occupied West Bank, where over 100 Palestinians have been killed since the start of the war, mostly during military raids and violent protests.
The Palestinian Health Ministry said three Palestinians were killed early Sunday as Israeli forces carried out raids across the occupied territory, where Israel says it has detained hundreds of Hamas members.