Israel says it had re-established control over the Gaza border and was planting mines where Hamas militants had toppled the barrier during their bloody weekend assault, after another night of relentless Israeli air raids on the enclave.
Israel's latest round of air strikes came after Hamas threatened to execute an Israeli captive every time Israel bombed a Palestinian home without warning.
The Israeli military also called up an unprecedented 300,000 reservists and imposed a blockade on the Gaza Strip, raising fears it planned a ground assault in response to the most audacious and deadly Hamas attack in decades.
The violence, which has claimed more than 1,600 lives, prompted international declarations of support and public demonstrations for both Israelis and Palestinians, and appeals for an end to the fighting and protection of civilians.
The significant escalation is the latest in a long-standing conflict between Hamas and Israel.
Hamas is a Palestinian military and political group, gaining power in the Gaza Strip since winning legislative elections there in 2006.
Hamas’s stated aim is to establish a Palestinian state, while refusing to recognise Israel’s right to exist.
Israeli TV channels said the death toll from the Hamas attack had climbed to 900 Israelis, with at least 2,600 injured, and dozens taken captive. Among the Israeli dead were 260 mostly young people gunned down at a desert music festival, where some of the hostages were abducted.
Israelis evacuate a site struck by a rocket fired from the Gaza Strip, in Ashkelon, southern Israel, on Monday. Source: AAP, AP / Ohad Zwigenberg
Gaza's Health Ministry on Tuesday said at least 770 Palestinians had been killed and 4,000 wounded in Israeli air strikes on the blockaded enclave since Saturday's attacks by Hamas.
At least another 18 people were killed and 100 injured in the West Bank since Saturday, the ministry added.
Apartment blocks, a mosque and hospitals were among the sites attacked, and the strikes destroyed some roads and houses, according to media reports and eyewitnesses.
Israel also bombed the headquarters of the private Palestinian Telecommunication Co., which could affect landline telephone, internet and mobile phone services.
The strikes continued into the night on Monday. The Israeli military said it hit targets in the Gaza Strip from the sea and air, including a weapons depot it said belonged to Islamic Jihad and Hamas targets along Gaza's coast line.
Hamas spokesperson Abu Ubaida issued the threat on Monday to kill Israelis among the dozens held captive after the surprise attack on Saturday morning. He said Hamas would execute an Israeli captive for every Israeli bombing of a civilian house without warning, and broadcast the execution.
There was no immediate response from the Israeli military to that threat. Israeli Foreign Minister Eli Cohen said more than 100 people had been taken captive by Hamas during the deadly cross-border incursion over the weekend.
Palestinians reported receiving calls and mobile phone audio messages from Israeli security officers telling them to leave areas mainly in the northern and eastern territories of Gaza, and warning that the army would operate there.
Dozens of people in Gaza City's Remal neighbourhood fled their homes.
"We took ourselves, children and grandchildren and daughters-in-law and we ran away. I can say that we became refugees. We don't have safety or security. What's this life? This is not a life," resident Salah Hanouneh, 73, said.
Gaza's Health Ministry said on Tuesday that at least 770 Palestinians had been killed and 4,000 wounded in Israeli air strikes on the blockaded enclave since Saturday. Source: AAP, ABACA, Press Association / Habboub Ramez/Alamy
The announcement that 300,000 reservists had been activated in just two days added to speculation that Israel could be contemplating a ground assault of Gaza, a territory it abandoned nearly two decades ago.
"We have never drafted so many reservists on such a scale," Hagari said. "We are going on the offensive."
Governments including Italy, Thailand and Ukraine reported that their citizens had perished in the Hamas attacks. In Washington, President Joe Biden announced that at least 11 Americans had been killed and it was likely United States citizens were among those held hostage.
The US said it was sending in fresh supplies of air defences, munitions and other security assistance to Israel.
United Nations Secretary-General Antonio Guterres said some 137,000 people were taking shelter with UNRWA, the UN agency that provides essential services to Palestinians.
The British, French, German, Italian and US governments issued a joint statement recognising the "legitimate aspirations" of the Palestinian people, and supporting equal measures of justice and freedom for Israelis and Palestinians alike.
They also said they would remain "united and coordinated" to ensure Israel can defend itself.
Egyptian President Abdel Fattah al-Sisi and his Turkish counterpart Tayyip Erdogan called on Hamas and Israel to immediately end violence and protect civilians, the Egyptian presidency said.
Qatari mediators held urgent calls to try to negotiate freedom for Israeli women and children seized by Hamas in exchange for the release of 36 Palestinian women and children from Israeli prisons.
Hamas, in its entirety, is designated as a terrorist organisation by countries including Australia, Canada, the United Kingdom and the United States.
Some countries list only its military wing as a terrorist group.
The UN though did not condemn Hamas in its entirety as a terrorist organisation, due to insufficient support from member states to do so during a 2018 vote.
