By Helen Regan, Abeer Salman, Lauren Izso and Lauren Said-Moorhouse

(CNN) — Gaza’s fragile ceasefire was shattered early Tuesday as Israel carried out deadly strikes across the enclave and Israeli Prime Minister Benjamin Netanyahu vowed to use “increasing military strength” against Hamas.

Gaza experienced its deadliest day in over 15 months on Tuesday, according to a CNN count, when Israel’s overnight bombardments struck multiple locations across the territory. More than 400 people were killed, according to Palestinian authorities, in the most extensive strikes since a months-long truce came into effect, with Israel’s Defense Minister Israel Katz declaring: “Tonight we returned to fighting in Gaza.”

The deal between Israel and Hamas was already hanging in the balance with phase one ending more than two weeks ago and all sides at loggerheads over a path forward that might see remaining Israeli hostages freed and a permanent peace secured.

Israel’s military and security agency said they were “currently conducting extensive strikes” on Hamas targets in Gaza. In response, Hamas accused Netanyahu of deciding to overturn the ceasefire agreement, and “putting the captives in Gaza at risk of an unknown fate.”

Speaking in Tel Aviv on Tuesday night, Netanyahu said Hamas refused to release hostages or accept a US proposal to extend the Gaza ceasefire, despite a pause in Israel’s military activity. “This is why I authorized yesterday the renewal of military action against Hamas,” he said.

Hamas spokesperson Abdul Latif Al-Qanou said the group wanted to see the ceasefire deal continue and had not rejected the US proposal on the table. He said Hamas is constantly in touch with mediators in the wake of renewed hostilities.

Gaza officials said more than 170 children were killed in the overnight attack, in what the United Nations children’s agency said was one of the largest single-day child death tolls in the past year globally.

“It’s been absolutely horrific,” said Dr. Razan Al-Nahhas, a physician volunteering with the Humanity Auxilium organization at the Al-Ahli Hospital in Gaza City. “Multiple explosions within just a span of a few minutes back-to-back.”

Videos obtained by CNN showed scenes of panic and chaos across Gaza as families desperately rushed wounded loved ones to overwhelmed hospitals and rescue workers transported patients in ambulances or on stretchers.

Many of the wounded were covered with bloodstained blankets, while others had their limbs wrapped in bloodied bandages. Several hospitals said the casualties were due to civilian homes being hit by the strikes.

Later on Tuesday, the Israeli military said it launched a “massive offensive” in Gaza and ordered civilians in multiple neighborhoods to evacuate, raising fears of further mass displacement.

‘They keep bringing more bodies’

In Gaza City, the volunteer doctor said the strikes began at around 2 a.m. local time and the Al-Ahli clinic had been receiving patients non-stop. Most of the casualties were children, she said.

“Babies, children all over the floor, bleeding from their heads, bleeding from their abdomens. Extremity injuries,” Al-Nahhas told CNN.

From a balcony in one of the hospital buildings, Al-Nahhas said she “can see all the bodies of the people that have been killed lined up,” saying at least 50 of them were “just wrapped in blankets” because there was no morgue.

It is a similar picture across the enclave. Israeli strikes have dealt a blow to “an exhausted healthcare system suffering from a shortage of medications and a severe lack of medical equipment,” the head of the enclave’s biggest hospital said.

Standing amid the rubble in the Deir al-Balah area of Gaza, resident Rajab Abu Sultan told CNN “we have been pulling the remains of children” from the debris. He added that the bodies being recovered were “all civilians, children” and that there had been “no prior warning.”

‘As long as necessary’

Israel’s resumption of strikes comes as renewed violence flares in the Middle East.

Dozens of people were reported killed after US President Donald Trump ordered “decisive” military action against Houthi rebels in Yemen, opening a new salvo against the Iran-backed group that has targeted shipping lanes in the Red Sea. The group on Tuesday said it would continue its attacks on American and Israeli interests until the hostilities in Gaza cease. Meanwhile, deadly cross-border attacks have underscored escalating tensions between Lebanon and Syria’s new Islamist-led government.

Israel had notified the Trump administration ahead of its strikes on Gaza, according to White House press secretary Karoline Leavitt.

Later on Tuesday the top US diplomat at the UN said that “the blame for the resumption of hostilities” in Gaza “lies solely with Hamas.” Charge d’affaires Dorothy Shea reiterated the sentiment at a UN Security Council meeting, saying that Hamas “has steadfastly refused every proposal and deadline they have been presented over the past few weeks.”

The Israeli military has continued to operate inside Gaza since the start of the ceasefire on January 19, but Tuesday’s airstrikes are the clearest sign that efforts to extend the truce have collapsed.

Netanyahu and Defense Minister Katz ordered the operation, accusing Hamas of “repeatedly” refusing to release hostages and rejecting all offers from United States presidential envoy Steve Witkoff and mediators.

Far-right Israeli politician Itamar Ben Gvir, who resigned as national security minister in January over the ceasefire deal, will rejoin the government along with his Otzma Yehudit, or Jewish Power, party after the Israeli military resumed the war in Gaza.

But former hostages and members of the Hostages and Missing Families Forum condemned the renewed offensive, saying it was detrimental to the remaining hostages, and urged the government to return to the negotiating table.

“Military operations endanger their lives directly,” recently-released hostage Sasha Troufanov said at a rally at Tel Aviv’s Hostage Square.

The Israeli strikes come days after the US put forward a new proposal that would secure the release of a handful of living hostages held by Hamas in exchange for a month-long extension of the ceasefire.

Under the US proposal, Israel would also lift its blockade of humanitarian aid into Gaza, a source familiar with the negotiations said.

Hamas said Friday it had responded to a proposal to extend the truce, “which included its approval” to release American-Israeli soldier Edan Alexander and the bodies of four dual nationals held hostage in Gaza.

But on Tuesday, Hamas leader Ezzat al-Rishq said the new airstrikes were a “death sentence” for the remaining Israeli hostages held in the enclave.

An Israeli official claimed the extensive attack in Gaza Tuesday was “preemptive” and said the strikes would “continue as long as necessary and will expand beyond airstrikes.”

The official declined to provide any details about what they claimed was Hamas’ “readiness to execute terror attacks, build up force and re-arm,” but said the strikes were targeting the group’s “mid-ranking military commanders, leadership officials and terrorist infrastructure.”

Hamas strongly rejected Israel’s claims that it violated the Gaza ceasefire and was preparing attacks on Israel, while seemingly opting not to respond militarily hours after Israel resumed fighting in Gaza.

The group said claims that it was preparing to strike Israeli forces were “baseless” pretexts to justify Israel’s return to war and designed to “mislead public opinion.”

Hamas is not known to have fired rockets at Israel in several weeks. It also appears to have refrained from striking Israel or its soldiers in Gaza since the ceasefire took effect on January 19.

This story has been updated with additional developments.

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