Israel said it had reclaimed control of the Gaza border, pounding the enclave with the fiercest air strikes in the 75-year history of its conflict with the Palestinians – despite a Hamas threat to execute a captive for each home hit.

Israel has vowed to take its "mighty revenge" since gunmen rampaged through its towns, leaving streets strewn with bodies in by far the deadliest attack in its history. It has called up hundreds of thousands of reservists and placed the Gaza Strip, crowded home to 2.3 million people, under a total siege.

Israeli media said the death toll from the Hamas attacks had climbed to 900 people, mostly civilians gunned down in their homes, on the streets or at a dance party, dwarfing the scale of any past attack apart from 9/11. Scores of Israelis were taken to Gaza as hostages, with some paraded through the streets.

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At least 770 Palestinians have been killed and 4,000 wounded in Israeli air strikes on the blockaded enclave since Saturday, Gaza's Health Ministry said. 

Among the dead are 140 children and 120 women, a ministry spokesperson said.

At the morgue in Gaza's Khan Younis hospital, bodies were laid on the ground on stretchers with their names written on their bellies. Medics called for relatives to pick up bodies quickly because there was no more space for the dead.

'No place is safe'

There were heavy casualties in a former municipal building struck while being used as an emergency shelter for displaced families.

"There is an extraordinary number of martyrs – people are still under the rubble, some friends are either martyrs or wounded," said Ala Abu Tair, 35, who had sought shelter there with his family after fleeing Abassan Al-Kabira near the border. "No place is safe in Gaza, as you see they hit everywhere."

Three Gaza journalists were killed when an Israeli missile hit a building while they were outside reporting. That brought the toll to six journalists killed in Gaza since Saturday.

Israeli strikes have leveled residential tower blocks and mosques and wrought widespread destruction in Gaza's Jabalia refugee camp, where many charred bodies were pulled from the rubble.

At one point the Israeli military advised Gaza civilians to flee to Egypt, only to issue a quick clarification confirming that the crossing was closed and there was no way out.

The Rafah crossing on Gaza's southern border with Egypt's Sinai peninsula has been closed until further notice, an Egyptian security source confirmed to dpa news agency.

Bombardments hit close to the crossing, three Egyptian security sources and a witness said.

As for Hamas operatives, they had "nowhere to hide in Gaza," said military spokesperson Rear Admiral Daniel Hagari. "We will reach them everywhere."

In Israel, there has still been no complete official count of the dead and missing from Saturday's attacks. In the southern town of Be'eri, where more than 100 bodies have been retrieved, volunteers in yellow vests and face masks solemnly carried the dead out of homes on stretchers.

"The thing I want the most is to wake up from this nightmare," said Elad Hakim, a survivor from a music festival where Hamas had killed 260 partygoers at dawn. "Everything was so amazing, the best party I've been to in my life, until it [went] from paradise to hell, in one second."

Gaza siege 'against international law'

Israel's next move could be a ground offensive into the Gaza Strip, territory it abandoned in 2005 and has kept under blockade since Hamas took power there in 2007. The total siege it announced on Monday would block even food and fuel from reaching the strip.

The World Health Organization called for a humanitarian corridor to be established into and out of the Gaza Strip.

United Nations Chief Antonio Guterres said he was "deeply distressed" by the siege announcement and warned Gaza's already dire humanitarian situation will now "only deteriorate exponentially."

The UN human rights chief Volker Turk said that imposing "sieges that endanger the lives of civilians by depriving them of goods essential for their survival is prohibited under international humanitarian law."

Military spokesperson Hagari said there had been no new infiltrations from Gaza since the previous day.

Israeli leaders will now have to decide whether to constrain their retaliation to safeguard the hostages. Hamas spokesperson Abu Ubaida issued the threat – to kill one Israeli captive for every Israeli bombing of a civilian house without warning, and to broadcast the killing.

Saturday's attacks and Israel's retaliation tore up the plans of diplomats in the Middle East at a crucial juncture, when Israel was on the verge of reaching an agreement to normalize relations with the richest Arab power, Saudi Arabia.

Israel's 'Swords of Iron' campaign

Western countries have strongly backed Israel. Arab cities have seen street demonstrations in support of the Palestinians. Iran, which supports Hamas, celebrated the attacks but denied playing a direct role in them.

Washington has pledged to send munitions and military equipment to back Israel and deployed an aircraft carrier group to the eastern Mediterranean.

Iran's Supreme Leader Ali Khamenei said the attacks had delivered a military and intelligence defeat to Israel that was beyond repair.

Prime Minister Benjamin Netanyahu has warned Israel's military campaign following Saturday's surprise mass onslaught was only the start of a sustained war to destroy Hamas and "change the Middle East."

The veteran leader at the helm of Israel's hard-right coalition also called for an "emergency government of national unity" after years of political crisis and bitter societal divisions.

The Israeli army has called up 300,000 reservists for its "Swords of Iron" campaign and massed tanks and other heavy armor both near Gaza, and on the northern border with Lebanon.

The military said its forces had largely reclaimed the embattled south and the border around Gaza in grueling battles with holdout Hamas fighters in around a dozen towns.

"Around 1,500 bodies of Hamas (fighters) have been found in Israel around the Gaza Strip," said army spokesman Richard Hecht.

The Israeli military said it had found no aerial infiltration from Syria or Lebanon after scrambling forces in response to a report it had received. 

Israel is on high alert for any spread of its Gaza war to the north, where it repelled a Lebanese border incursion.

Hamas's 'Operation Al-Aqsa Flood'

Hamas has called on "resistance fighters" in the West Bank and in Arab and Islamic nations to join what it has dubbed "Operation Al-Aqsa Flood."

Global powers and regional governments including Egypt, Turkey and Gulf states, have engaged in frantic diplomacy seeking to prevent any further escalation.

Saudi Arabia's de facto ruler Crown Prince Mohammed bin Salman told Palestinian President Mahmud Abbas that the kingdom was working to ensure the conflict does not spread across the region, state media reported.

Türkiye's President Recep Tayyip Erdogan warned Israel against "indiscriminately" attacking civilians and also delivered measured criticism of Hamas, urging both sides to respect the "ethics" of war.

France said it was against suspending aid that "directly" benefits the Palestinians, after the European Union said it was reviewing developments in the conflict.

The United Nations humanitarian office said that nearly 200,000 people or nearly a tenth of the population, have fled their homes in Gaza since the start of hostilities. 

"Displacement has escalated dramatically across the Gaza strip, reaching more than 187,500 people since Saturday. Most are taking shelter in schools," Jens Laerke, OCHA spokesperson, told a Geneva briefing, saying further displacement was expected as clashes continue.

A World Health Organization spokesperson said it had reported 13 attacks on health facilities in the Gaza strip since the weekend and said that its medical supplies stored there had already been used up.

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