TEL AVIV — Some 1,100 people have been killed in Israel and Gaza as Israel's military battled to drive Hamas fighters out of southern towns and seal its borders Monday following a large-scale assault by the militant group that began early Saturday.

Fears of a ground invasion of Gaza are growing after Israeli Prime Minister Benjamin Netanyahu threatened to turn the besieged Palestinian enclave into a “deserted island”. The Israeli military says it has gathered 100,000 reserve troops near the border.

Hamas’s operation came after widespread Israeli settler attacks, increased tensions at the Al-Aqsa Mosque in occupied East Jerusalem and a record number of Palestinians killed.

At least 700 people have reportedly been killed in Israel — a staggering toll on a scale the country has not experienced in decades — and more than 400 have been killed in Gaza. Palestinian groups claimed to be holding over 130 captives from the Israeli side.

More than two days after Hamas launched its unprecedented incursion out of Gaza, Israeli forces were still battling militants holed up in several locations.

As Monday began, the military said it was fighting Hamas in “seven to eight” places in southern Israel.

Military spokesperson Richard Hecht said it was taking longer than expected to repel the incursion because there were still multiple breaches in the border, which Hamas could be using to bring in more fighters and weapons. “We thought this morning we'd be in a better place,” Hecht said.

The Israeli Defense Forces said that 70 additional militants infiltrated Be'eri kibbutz, which the military has been unable to wrest from Hamas, overnight.

The violence is the biggest escalation between the two sides for decades, with some analysts claiming Israel was caught off guard.

Meanwhile, Israel hit more than 1,000 targets in Gaza, its military said, including airstrikes that leveled much of the town of Beit Hanoun in the enclave’s northeast corner.

Israeli Rear Adm. Daniel Hagari told reporters Hamas was using the town as a staging ground for attacks. There was no immediate word on casualties, and most of the community’s population of tens of thousands likely fled beforehand.

The Israeli military estimated 1,000 Hamas fighters took part in Saturday’s initial incursion. The high figure underscored the extent of planning by the militant group ruling Gaza, which has said it launched the attack in response to mounting Palestinian suffering under Israel’s occupation and blockade of Gaza.

Hamas and the smaller Islamic Jihad group claimed to have taken captive more than 130 people from inside Israel and brought them into Gaza, saying they would be traded for the release of thousands of Palestinians imprisoned by Israel. The announcement, though unconfirmed, was the first sign of the scope of abductions.

The captives are known to include soldiers and civilians, including women, children and older adults, mostly Israelis but also some people of other nationalities. The Israeli military said only that the number of captives is “significant.”

Hamas has captured a new group of Israeli soldiers, according to Al Jazeera, but Israel has not confirmed this.

The Israeli military was evacuating at least five towns close to Gaza, while the UN said more than 123,000 Gazans had been displaced by the fighting.

“Over 123,538 people, have been internally displaced in Gaza, mostly due to fear, protection concerns and the destruction of their homes,” said the UN’s humanitarian agency, OCHA.

Some European Union member states have begun evacuating their citizens from Israel after the outbreak of fighting with Hamas.

On Monday morning, Hungarian MP Balázs Orbán said his country had evacuated 215 people in a joint rescue operation.

"Our priority is the safety of our people," he said, thanking Israel, Cyprus, Greece, Turkey, Bulgaria and Romania for their cooperation.

Poland has also started evacuating its citizens from Israel, with the first plane carrying around 120 people landing in Warsaw early on Monday.

"The first people evacuated from Israel are already in Poland. I would like to thank [our] soldiers for carrying out the operation efficiently. You are the best," Polish defense minister Mariusz Blaszczak tweeted.

On Sunday, Blaszczak said some 200 Polish tourists, including children on a school trip, waiting to leave Israel.

In Gaza, residents feared further escalation.

As of late Sunday, Israeli airstrikes had destroyed 159 housing units across Gaza and severely damaged 1,210 others. The UN agency for Palestinian refugees, UNRWA, said a school sheltering more than 225 people took a direct hit.

In the Palestinian city of Rafah in southern Gaza, an Israeli airstrike early Monday killed 19 people, including women and children, said Talat Barhoum, a doctor at the local Al-Najjar Hospital. Barhoum said aircraft hit the home of the Abu Hilal family, and that one of those killed was Rafaat Abu Hilal, a leader of a local armed group. The strike caused damage to surrounding homes.

Over the weekend, another airstrike on a home in Rafah killed 19 members of the Abu Outa family, including women and children, when they were huddling on the ground floor in the southern Gaza city of Rafah, survivors said.

The declaration of war was largely symbolic, said Yohanan Plesner, the head of the Israel Democracy Institute, a think tank, but it “demonstrates that the government thinks we are entering a more lengthy, intense and significant period of war.”

Israel has carried out major military campaigns over the past four decades in Lebanon and Gaza that it portrayed as wars, but without a formal declaration.

The presence of hostages in Gaza complicates Israel’s response. Israel has a history of making heavily lopsided exchanges to bring captive Israelis home.

An Egyptian official said Israel sought help from Cairo to ensure the safety of the hostages. Egypt also spoke with both sides about a potential cease-fire, but Israel was not open to a truce “at this stage,” according to the official, who asked not to be identified because he was not authorized to brief media.

In northern Israel, a brief exchange of strikes with Lebanon’s Hezbollah militant group fanned fears that the fighting could expand into a wider regional war. Hezbollah fired rockets and shells Sunday at Israeli positions in a disputed area along the border, and Israel fired back using armed drones. The Israeli military said the situation was calm after the exchange.

Elsewhere, six Palestinians were killed in clashes with Israeli soldiers Sunday around the West Bank.

Human Rights Watch (HRW) has condemned both Israel and Hamas for violating international law, calling for an end to "further abuses".

“Deliberate killings of civilians, hostage-taking, and collective punishment are heinous crimes that have no justification,” said Omar Shakir, Israel and Palestine Director at HRW, a US-based NGO.

“The unlawful attacks and systematic repression that have mired the region for decades will continue, so long as human rights and accountability are disregarded,” he added in a statement sent to Euronews on Monday.

HRW said Palestinians have recently faced "unprecedented repression," noting Israeli authorities had killed more Palestinians in the occupied West Bank in the first nine months of 2023 than in any year since the UN began systematically recording fatalities in 2005.

In previous outbreaks of violence, HRW said it has documented "serious violations of the laws of war by Israeli forces and by Palestinian armed groups."

It also claimed Israel has repeatedly carried out indiscriminate airstrikes that killed scores of civilians and targeted civilian infrastructure, including destroying high-rise Gaza towers full of homes and businesses, with no evident military targets in the vicinity.

For 17 years, Israel has shut Gaza off from the outside world, banning Palestinians in the tiny pocket of land from traveling.

Haaretz, one of Israel's largest newspapers, has said Israeli Prime Minister Netanyahu is to blame for the violence that broke out on Saturday.

"The disaster that befell Israel on the holiday of Simchat Torah is the clear responsibility of one person: Benjamin Netanyahu," its Editorial Board wrote.

"The prime minister, who has prided himself on his vast political experience and irreplaceable wisdom in security matters, completely failed to identify the dangers he was consciously leading Israel into when establishing a government of annexation and dispossession when appointing Bezalel Smotrich and Itamar Ben-Gvir to key positions, while embracing a foreign policy that openly ignored the existence and rights of Palestinians."

Haaretz, markets itself as a center-left progressive newspaper, it has the third largest circulation in Israel and is read widely overseas. — Agencies