JERUSALEM / CAIRO >> Israeli airstrikes pounded Gaza and killed more than 400 people, Palestinian health authorities said today, in an onslaught across the enclave that ended weeks of relative calm after talks to secure a permanent ceasefire stalled.

Israel and Palestinian militant group Hamas each accused the other of breaching the truce, which had broadly held since January, offering respite from war for the 2 million inhabitants of Gaza, where most buildings have been reduced to rubble.

Hamas, which still holds 59 of the 250 or so hostages Israel says the group seized in its October 7, 2023 attack, accused Israel of jeopardising efforts by mediators to negotiate a permanent deal to end the fighting, but the group made no threat of retaliation.

Israeli Prime Minister Benjamin Netanyahu said he ordered strikes because Hamas had rejected proposals to secure a ceasefire extension during faltering talks.

“Israel will, from now on, act against Hamas with increasing military strength,” the prime minister’s office said in a statement.

The strikes hit houses and tent encampments from the north to the south of the Gaza Strip, and Israeli tanks shelled from across the border line, witnesses said. Gaza’s Hamas-run health ministry said 404 people had been killed in one of the biggest single-day tolls since the war erupted.

“It was a night of hell. It felt like the first days of the war,” said Rabiha Jamal, 65, a mother of five from Gaza City, who said her building shook as the explosions began.

Families in Beit Hanoun in the northern Gaza Strip and eastern areas of Khan Younis in the south fled their homes, some on foot, others in cars or rickshaws, carrying some of their belongings after the Israeli military issued evacuation orders warning the areas were “dangerous combat zones”.

Egypt and Qatar, mediators in the ceasefire deal along with the U.S., condemned the Israeli assault.

The U.N. emergency relief coordinator, Tom Fletcher, said the “modest gains” made during the ceasefire had been destroyed.

He said humanitarian aid and commercial essentials must be allowed to enter Gaza. Israel has halted aid deliveries into Gaza for over two weeks, exacerbating a humanitarian crisis.

However, Dorothy Shea, acting U.S. 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 airstrikes earned Netanyahu a political boost at home. Former National Security Minister Itamar Ben-Gvir, who left the government over disagreements about the Gaza ceasefire, is rejoining the coalition after the resumption of Israeli strikes, a statement said, strengthening Netanyahu’s government.

But former hostages and the families of some still held in Gaza expressed outrage over the resumption of war.

Released hostage Yarden Bibas, whose wife and two young sons were slain in captivity, said on Facebook:

“Israel’s decision to return to fighting brings me back to Gaza, to the moments where I heard the sounds of explosions around me and where I feared for my life as I was afraid that the tunnel where I was being held would collapse … Military pressure endangers hostages, an agreement brings them back.”

In Gaza, witnesses contacted by Reuters said Israeli tanks shelled areas in Rafah in the south. Bewildered children sat next to bagged-up belongings, ready to flee north again having returned to Rafah with the ceasefire.

In hospitals strained by 15 months of bombardment, piles of bodies in white plastic sheets smeared with blood were stacked up as casualties were brought in. The health ministry said many of the dead were children, and 562 people were injured.

Among the Hamas officials killed in the airstrikes were Essam Addalees, the de facto head of the Hamas government, Ahmed Al-Hetta, deputy justice minister and Mahmoud Abu Watfa, the head of the Hamas-run security services, Hamas said.

As Israel launched its operation in Gaza, its forces have pressed on with an operation in the occupied West Bank and Israeli jets have struck targets in southern Lebanon and Syria in recent days.

Negotiating teams from Israel and Hamas had been in Doha as mediators sought to bridge the gap between the two sides after the end of an initial phase in the ceasefire, which saw 33 Israeli hostages and five Thais released in exchange for some 2,000 Palestinian prisoners.

Israel had been pressing for the return of the remaining hostages in exchange for a truce until after the Muslim fasting month of Ramadan and the Jewish Passover holiday in April.

However, Hamas has insisted on moving to negotiations for a permanent end to the war and a full withdrawal of Israeli forces, under the terms of the original ceasefire agreement.

Today, Hamas spokesperson Abdel-Latif Al-Qanoua told Reuters the group was still in touch with mediators, and it was keen to complete the implementation of the original deal.

Egyptian mediators were engaged in intense contacts to salvage the ceasefire, two Egyptian security sources said.

Much of Gaza now lies in ruins after the war, which erupted on October 7, 2023 when Hamas-led gunmen attacked Israel, killing some 1,200 people, according to Israeli tallies.

The Israeli campaign in Gaza has killed more than 48,000 people, say Palestinian health authorities, and destroyed much of the housing and infrastructure in the enclave.