The renewed attacks shattered the fragile ceasefire, plunging the besieged Strip into further devastation.
Witnesses reported massive explosions and rising plumes of smoke as Israeli warplanes pounded residential areas, adding to the humanitarian crisis in the densely populated territory.
In Khan Yunis, AFP footage showed people rushing stretchers with wounded people, including young children, to the Nasser Hospital. Bodies covered with white sheets were also taken to the hospital's mortuary.
Mohammed Jarghoun, 36, was sleeping in a tent near his destroyed house in Khan Yunis when huge blasts waked him.
"I thought they were dreams and nightmares, but I saw a fire in my relatives' house. More than 20 martyrs and wounded, most of them children and women."
Ramez Alammarin, 25, described carrying children to a hospital southeast of Gaza City.
'Hell will break loose'
"They unleashed the fire of hell again on Gaza," he said of Israel, adding that "bodies and limbs are on the ground, and the wounded cannot find any doctor to treat them.
"They bombed a building in the area and there are still martyrs and wounded under the rubble... fear and terror. Death is better than life."
Mohammed Zaqut, head of the health ministry in Gaza, said "at least 330 deaths" had been recorded, "most of them Palestinian women and children". Later the toll was updated to 413.
He said there were "hundreds of wounded, dozens of them in critical condition".
Two Hamas sources told AFP that a stike in Gaza City killed General Mahmud Abu Watfa, who headed the group's interior ministry in the territory.
Israel ordered all schools near the Gaza border to shut.
The White House confirmed that Israel consulted US President Donald Trump's administration before launching the wave of strikes.
Displaced Palestinians who fled al-Mughraqa town arrive at the Nuseirat refugee camp in the central Gaza Strip. AFP
No phase two
Hamas accused Israeli Prime Minister Benjamin Netanyahu of deciding to "resume war" after a deadlock on extending the truce and warned that the return to fighting could be a "death sentence" for captives still alive in Gaza.
In a statement, Hamas said: "Netanyahu and his extremist government have decided to overturn the ceasefire agreement.
"Netanyahu's decision to resume war is a decision to sacrifice the occupation's prisoners and impose a death sentence on them," it said, accusing him of using the war as a political "lifeboat" to stay afloat amid domestic crises.
Netanyahu's office claimed the operation was ordered after "Hamas's repeated refusal to release our captives, as well as its rejection of all of the proposals it has received from US Presidential Envoy Steve Witkoff and the mediators.
An Israeli official told AFP the occupation army would "continue as long as necessary" and was expected to "expand beyond air strikes".
Mediated by Qatar, Egypt and the United States, the initial phase of the ceasefire took effect on January 19, largely halting more than 15 months of the Israeli war on Gaza since October 7, 2023.
That first phase ended in early March, and while both sides have since refrained from full-blown war, they have been unable to agree on the next steps for truce talks.
Israel has also carried out strikes on Gaza, but not on the scale of Tuesday's operation.
US envoy Witkoff told CNN on Sunday he had offered a "bridge proposal" that would see five living captives, including Israeli-American Edan Alexander, released in return for freeing a "substantial amount of Palestinian prisoners" from Israel jails.
Hamas had said it was ready to free Alexander and the remains of four others.
Witkoff claimed Hamas had provided "an unacceptable response" and "the opportunity is closing fast", as the Paletinian resistance gtoup has consistently demanded negotiations for the second phase, as stipulated by the deal instead of prolonging phase one as Israel demands.
Former US president Joe Biden had outlined a second phase which would involve the release of remaining living captives, the withdrawal of all Israeli forces left in Gaza and the establishment of a lasting ceasefire.
Israel, however, seeks to extend the first phase until mid-April, insisting any transition to the second phase must include "the total demilitarisation" of Gaza and the removal of Hamas, which has controlled the territory since 2007.
White claimed Press Secretary Karoline Leavitt confirmed that Trump's administration had been consulted ahead of Israel's Tuesday operation.
"As President Trump has made it clear, Hamas, the Houthis, Iran, all those who seek to terrorise not just Israel, but also the United States of America, will see a price to pay -- all hell will break loose," she said in the televised interview.
During the first phase of the truce agreement, Hamas released 33 captives, including eight deceased, and Israel freed around 1,800 Palestinian detainees.
A Palestinian woman carries a baby as families leave the eastern sector of the Gaza Strip on the border with Israel following Israeli airstrikes that targeted northern and other parts of Gaza in the early hours. AFP
The talks have been deadlocked, and Israel has cut aid and electricity to the territory.
"It's so hard for me to think about what they're (hostages) going through right now because I know that feeling," freed Israeli captive Omer Shem Tov said in a recently released video.
"It's a terrible feeling and it has to stop as soon as possible."
Israel's war on Gaza has killed at least 48,572 people, also mostly children and women.
A man looks at the rubble of a school-turned-camp after an Israeli strike in Gaza City. AFP
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