Benjamin Netanyahu has vowed to destroy Hamas after renewing Israel's air strikes on the Gaza Strip.
The Israeli Prime Minister defended the resumption of airstrikes in the heavily bombarded enclave, saying that negotiations on restoring the ceasefire would continue "only under fire".
The ceasefire-breaking move was met with condemnation from charities and other countries in the region, including Turkey and the UAE.
Hamas, which still holds 59 of the 250 hostages seized in its October 7 attack, accused Israel of jeopardising efforts by mediators to negotiate a permanent deal to end the fighting.
Israeli Prime Minister Benjamin Netanyahu
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Palestinians make their way to flee their homes, after the Israeli army issued evacuation orders for a number of neighborhoods
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Israeli soldiers operate at a post on the Israeli side of the border between Israel and Gaza
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Palestinians make their way to flee their homes
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Gaza hospitals already reeling from weeks of an aid blockade, medics and health authorities said, as ambulances ferried in hundreds of badly injured survivors.
Mohammad Qishta, a Medicins Sans Frontieres emergency doctor working at Nasser Hospital in Khan Younis, told reporters: "We received no less than 400 cases in less than two hours.
"There were some serious cases such as burns...third degree burns on the face, amputations, wounds on the head, wounds on the chest."
Netanyahu said military pressure on Hamas was a "critical condition" for securing the release of hostages held by the Islamist terror group, adding: "This is just the beginning."
LATEST DEVELOPMENTS FROM GAZA:
Tom Fletcher addresses attendees via video link during the Security Council meeting
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Soldiers sit on top of APC's, at the Israel-Gaza border, in Israel
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Children look on as people walk amid the rubble of a building destroyed in an overnight Israeli strike in Jabalia,
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UN Under-Secretary-General Tom Fletcher spoke at a Security Council briefing after Palestinian health authorities said Israeli airstrikes pounded Gaza, killing more than 400 people.
Fletcher said: "Overnight our worst fears materialized. Airstrikes resumed across the entire Gaza Strip. Unconfirmed reports of hundreds of people killed...once again, the people of Gaza are living in abject fear."
"Humanitarian workers remain on the ground...ready to provide life-saving support to survivors and to carry out humanitarian operations...We must be allowed to do so."
It comes after Israel halted aid deliveries into Gaza for more than two weeks, exacerbating a humanitarian crisis.
Israelis take part in a protest against the government and its head Israeli Prime Minister Benjamin Netanyahu and demanding the release of all hostages
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Palestinians make their way to flee their homes, after the Israeli army issued evacuation orders
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Palestinians inspect the site of an Israeli strike on a residential building, in Deir Al-Balah in the central Gaza Strip
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However, Dorothy Shea, acting US ambassador to the United Nations, said the blame for the resumption of Gaza hostilities "lies solely with Hamas" and expressed support for Israel in its next steps.
The war erupted after Hamas-led gunmen attacked Israel, killing some 1,200 people.
Israel's campaign in Gaza has killed more than 48,000 people, Gaza's Hamas-run Health Ministry has claimed.
