Jerusalem and Gaza CNN  — 

Israel has formally declared war on Hamas, setting the stage for a major military operation in Gaza as fighting continues to rage on Israeli soil.

Tanks and personnel carriers could be seen on the move near the Israel-Gaza border on Sunday, after Hamas – an Islamist militant group – launched an unprecedented and highly coordinated surprise assault this weekend that has so far killed over 700 Israelis.

Saturday was the deadliest day in decades for Israel and came after months of surging violence between Palestinians and Israelis, with the long-running conflict now heading into uncharted and dangerous new territory.

Questions remain over how the Israeli military and intelligence apparatus appeared to be caught off guard in one of the country’s worst security failures.

Hamas claims to be holding “over 100” Israeli hostages, including high-ranking officers, and continued to fire rockets into Israel throughout Sunday. Another Palestinian armed group, called Islamic Jihad, said on Sunday it is holding at least 30 hostages in Gaza.

Israeli Prime Minister Benjamin Netanyahu has vowed retaliation, warning his country would take “mighty vengeance” and was readying for “a long and difficult war.”

He urged Palestinians living in Gaza to “leave now.”

Over 400 Palestinians have been killed in Gaza as Israel responds with airstrikes in the densely-inhabited enclave.

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Throughout the bloody weekend, Hamas launched thousands of rockets from the Gaza Strip into Israel – making direct hits on multiple locations inside the country including Tel Aviv – while armed terror groups entered Israel and infiltrated military bases, towns and farms, shooting at civilians and taking hostages.

Photos released by the Israeli foreign ministry showed dozens of bodies in the aftermath of a Hamas attack on a music festival near the Israel-Gaza border, which emergency responders said left at least 260 dead.

As Israeli forces clashed on the ground with Hamas fighters, Israeli airstrikes blasted what it said were Hamas-associated locations.

The Israel Defense Forces (IDF) said it had struck over 400 targets in the small enclave, including 10 towers that it said were used by Hamas and “a number of terrorist squads in the area surrounding the Gaza Strip.”

Palestinian authorities say 78 children are among the dead, and 2,300 others wounded.

According to Netanyahu, Israel’s “first phase” of retaliation has ended with the “destruction of the majority of the enemy forces that penetrated our territory.” It will be followed by an “offensive formation,” he said.

His government has decided to stop the supply of electricity, fuel and goods to Gaza.

Eyad Baba/AFP/Getty Images
Fire and smoke rises above buildings during an Israeli air strike in Gaza City on October 8, 2023.
Ali Jadallah/Anadolu Agency/Getty Images
Flames rise in Burc Vatan shopping mall in Gaza following bombing of Israeli forces with warplanes.

Hamas has warned against measures in Gaza, alluding to hostages held in the area.

In a recorded audio message Saturday, Abu Obaida spokesman for the Al Qassam Brigades, the armed wing of Hamas, said: “What happens to the people of the Gaza Strip will happen to them and beware of miscalculation.”

Civilians taken hostage include “not only soldiers but civilians, children, grandmothers,” Israeli Defense Forces spokesman Lt. Col. Richard Hecht told a briefing on Sunday. “We have lost soldiers, we have lost commanders, we have lost a lot of civilians.”

It has been more than 17 years since an Israeli soldier was taken as a prisoner of war in an assault on Israeli territory. And Israel has not seen this kind of infiltration of military bases, towns and kibbutzim since town-by-town fighting in the 1948 war of independence.

Oded Balilty/AP
Israelis inspect the rubble of a building a day after it was hit by a rocket fired from the Gaza Strip, in Tel Aviv, Israel, on Sunday.

On Sunday, Hecht, the IDF spokesman, said Israeli forces had neutralized most of the significant battles that took place in the settlement of Otef, but there are still ongoing operations in numerous other parts of the country.

The IDF’s goal for the next 12 hours is to “end the Gaza enclave … and kill all the terrorists in our territory,” he said.

The IDF is evacuating more than 20 communities adjacent to the Gaza security fence, and searching the area for any Hamas militants left. It is also seeking to control breaches in the fence.

Asked by a journalist about the intelligence failure that had allowed such a large scale attack to occur, Hecht said: “This is not a question for now … I am sure that will be a big discussion down the road.”

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‘No warning of any kind’

The highly coordinated assault, which began Saturday morning, was unprecedented in its scale and scope and came on the 50th anniversary of the 1973 War in which Arab states blitzed Israel on Yom Kippur, the holiest day of the Jewish calendar.

“We had no warning of any kind, and it was a total surprise that the war broke out this morning,” Efraim Halevy, the former head of Mossad, Israel’s Intelligence Service, told CNN.

The number of rockets fired by Palestinian militants was at a scale “never seen before,” Halevy said, and this was “the first time” that Gaza has been able to “penetrate deep into Israel and to take control of villages.”

Amir Cohen/Reuters
Israel's Iron Dome anti-missile system intercepts rockets launched from the Gaza Strip, as seen from Ashkelon in southern Israel October 7, 2023

It is rare for Palestinian militants to be able to make it into Israel from Gaza which is sealed off and heavily watched by Israel’s military. Gaza is one of the most densely packed places in the world, an isolated coastal enclave of almost 2 million people crammed into 140 square miles.

Governed by Hamas, the territory is largely cut off from the rest of the world by an Israeli blockade of Gaza’s land, air and sea dating back to 2007. Egypt controls Gaza’s southern border crossing, Rafah. Israel has placed heavy restrictions on the freedom of civilian movement and controls the importation of basic goods into the narrow coastal strip.

Fighting between the two sides has surged in the last two years. The violence has been driven by frequent Israeli military raids in Palestinian towns and cities, which Israel has said are a necessary response to a rising number of attacks by Palestinian militants on Israelis.

They also come at a moment of deep division in Israel, months after the country’s right-wing government pushed through a contentious plan to reduce the power of the country’s courts, sparking a social, political and military crisis.

Western states condemned the Hamas attack on Saturday and pledged support for Israel while Arab states, including those that have recognized Israel, called for calm.

United States President Joe Biden spoke to Israeli Prime Minister Benjamin Netanyahu on Saturday and said that Washington “unequivocally condemns this appalling assault against Israel by Hamas terrorists from Gaza.”

Saudi Arabia, which is holding talks with the US to potentially normalize relations with Israel, said it is following closely the “unprecedented” situation and called on “both sides to immediately stop the escalation,” according to a statement by the Saudi foreign ministry on X.

Ibraheem Abu Mustafa/Reuters
Palestinians search for casualties under the rubble of a house destroyed in Israeli strikes in Khan Younis, in the southern Gaza Strip.

Pleas for release of hostages

Israelis are sharing photos of friends and family who they say have been kidnapped by Hamas militants, many of them women and children.

One Israeli mother told CNN she had been on the phone with her children, aged 16 and 12, who were home alone when they heard gunshots outside and people trying to enter.

“They were scared to death. I can’t even imagine what they felt. And I wasn’t there to help,” said the mother, who was away from the home at the time. CNN is not identifying the mother and her children for safety reasons.

Then, over the phone, she heard the door break down.

“I heard terrorists speaking in Arabic to my teenagers. And the youngest saying to them ‘I’m too young to go,’” the mother said. “And the phone went off, the line went off. That was the last time I heard from them.”

Another Israeli resident Yoni Asher told CNN his wife, who was visiting near the Gaza border with their young daughters, was among those abducted. On Saturday he tracked her phone and saw it was located in Gaza; later that day he said he recognized her in a viral clip of people loaded into the back of a truck flanked by Hamas militants.

Several people were taken hostage during an attack by Hamas militants on an Israeli music festival near the Israel-Gaza border. One video on social media showed an Israeli woman being kidnapped, hoisted onto the back of a motorcycle and driven away as her boyfriend was apprehended. Another clip pictured a German-Israeli woman who was taken from the festival being paraded around Gaza, unconscious and motionless.

An Israel Police spokesperson has told CNN that family members who wish to report their loved ones as missing to come to the nearest police station when it’s safe to leave their homes. The police suggested relatives bring photos and personal items from which DNA samples can be extracted to help with identification.

Correction: This article has been updated to correct a reference to the Israeli political-security cabinet's aim to degrade the capabilities of Hamas and other organizations in Gaza.

CNN’s Mohammad Tawfeeq, Jonny Hallam, Kareem Khadder, Paul P. Murphy, Lauren Iszo, Ibrahim Dahman, Amir Tal, Abeer Salman, Richard Allen Greene, Hande Atay Alam, Clarissa Ward and Brent Swails contributed reporting.