Israel’s military ordered a complete siege on the Gaza Strip on Monday, halting deliveries of food, fuel and supplies to its 2.3 million people as it pounded the Hamas-ruled territory with waves of airstrikes in retaliation for the militants’ bloody weekend incursion.

More than two days after Hamas launched its surprise attack, the Israeli military said it had largely gained control in its southern towns where it had been battling Hamas gunmen. Israel’s vaunted military and intelligence apparatus was caught completely off guard by Hamas, resulting in heavy battles in its streets for the first time in decades.

Also read: Israel intensifies Gaza strikes and battles to repel Hamas, with over 1,100 dead in fighting so far

Israeli tanks and drones were deployed to guard breaches in the Gaza border fence to prevent new incursions. Thousands of Israelis were evacuated from more than a dozen towns near Gaza, and the military summoned 300,000 reservists — a massive mobilization in a short time.

The moves, along with Israel’s formal declaration of war on Sunday, pointed to Israel increasingly shifting to the offensive against Hamas, threatening greater destruction in the densely populated, impoverished Gaza Strip.

Also read: What to know as Israel declares war, bombards Gaza Strip after unprecedented Hamas attack

A major question remains whether Israel will launch a ground assault into the tiny Mediterranean coastal territory, a move that in the past has brought intensified casualties.

Israel and Hamas have had repeated conflicts in past years, often sparked by tensions around a Jerusalem holy site. This time, the context has become potentially more explosive, and both sides talk of shattering with violence a years-long Israeli-Palestinian deadlock left by the moribund peace process.

Also read: Israel intensifies its strikes and vows to besiege Gaza as it scours south for Hamas fighters

Israel has been stunned by a surprise attack and death toll unseen since the 1973 war with Egypt and Syria. That is fomenting calls to crush Hamas no matter the cost, rather than continuing to try to bottle it up in Gaza. Israel is run by its most hard-right government ever, dominated by ministers who adamantly reject any Palestinians statehood.

Hamas, in turn, says it is ready for a long battle to end an Israeli occupation it says is no longer tolerable. Desperation has grown among Palestinians, many of whom see nothing to lose under unending Israeli control and increasing settler depredations in the West Bank, the blockade in Gaza and what they see as the world’s apathy.

“I ask you to stand firm because we are going to change the Middle East,” Israeli Prime Minister Benjamin Netanyahu told authorities from the south Monday. “I know you have been through terrible and difficult things. What Hamas will go through will be difficult and terrible … we have only just begun.”

In the early evening, the sound of explosions echoed over Jerusalem when a volley of rockets fired from Gaza hit two neighborhoods – a sign of Hamas’s reach. Israeli media said seven were wounded.

On Sunday, Israeli strikes leveled much of the Gaza town of Beit Hanoun, which Israel said Hamas was using as a staging ground. On Monday, the Israeli military blared messages to residents to evacuate Rimal, a residential and commercial district of central Gaza City where offices of The Associated Press and other international media are located, a signal that heavy strikes were to come.

As Israel hit more than 1,000 targets in Gaza, Palestinian militants continued firing barrages of rockets, setting off air raid sirens in Jerusalem and Tel Aviv.

Around 700 people, including 73 soldiers, have been killed in Israel, according to Israeli media outlets, citing rescue service — a staggering toll by the scale of its recent conflicts. The Gaza Health Ministry said 493 people, including 78 children and 41 women, were killed in the territory. Thousands have been wounded on both sides.

Palestinian militant groups claimed to be holding over 130 people abducted in Israel and dragged into Gaza. The armed wing of Hamas claimed on its Telegram channel that four of them were killed in Israeli airstrikes. That could not be independently confirmed.

Israeli Defense Minister Yoav Gallant ordered a “complete siege” on Gaza, saying authorities would cut electricity and block the entry of food and fuel.

Gallant said Israel was at war with “human animals,” using the kind of dehumanizing language often employed by both sides at times of soaring tensions.

Israel and Egypt have imposed a blockade on Gaza of varying strictness since Hamas seized power in 2007. In recent years Israel has provided limited electricity and allowed the import of food, fuel and some consumer goods, while heavily restricting travel in and out.

The Israeli seal will leave Gaza almost entirely dependent on its crossing into neighboring Egypt at Rafah, where cargo capacities are lower than other crossings into Israel.

An Egyptian military official, speaking on condition of anonymity because he was not authorized to talk to the press, said more than 2 tons of medical supplies from the Egyptian Red Crescent were sent to Gaza and efforts were underway to organize food, and other deliveries, but the question of allowing in fuel was not yet decided.

Israeli Rear Adm. Daniel Hagari told reporters that Israeli bombardment was moving from district to district to destroy houses and buildings Israel says are being used by Hamas. Israel is planning to hit thousands of targets, he said. He said “hundreds” of Hamas militants were buried under rubble of buildings destroyed by Israel in the past 48 hours. His claims of the numbers – and his characterization of the dead as Hamas – could not be confirmed.

In the southern Gaza city of Rafah, 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.

The U.N. said more than 123,000 people have fled their homes in Gaza – many after Israeli warnings of imminent bombardment. The U.N. agency for Palestinian refugees, UNRWA, said a school sheltering more than 225 people took a direct hit. It did not say where the fire came from.

Meanwhile, after about 48 hours of pitched battles, Hagari said the military has “control” of its border communities in southern Israel. He said 15 of 24 border communities have been evacuated, with the rest expected to be emptied in the coming day.

Earlier, Hamas spokesman Abdel-Latif al-Qanoua told The Associated Press over the phone that the group’s fighters continued to battle outside Gaza and had captured more Israelis as recently as Monday morning.

He said the group aims to free all Palestinian prisoners held by Israel, which in the past has agreed to lopsided exchange deals in which it released large numbers of prisoners for individual captives or even the remains of soldiers.

Among the captives are soldiers and civilians, including women, children and older adults, mostly Israelis but also some people of other nationalities. Egypt’s state-run Al-Ahram newspaper said Monday that Egyptian officials are trying to mediate a release of Palestinian women in Israel’s prisons in exchange for Israeli women captured by militants.

Mayyan Zin, a divorced mother of two, said she learned that her two daughters had been abducted when a relative sent her photos from a Telegram group showing them sitting on mattresses in captivity. She then found online videos of a chilling scene in her ex-husband’s home: Gunmen who had broken in speak to him near the two weeping daughters, Dafna, 15, and Ella, 8. Another video showed the father being taken into Gaza.

“Just bring my daughters home and to their family. All the people,” Zin said.

Hamas has ruled Gaza since driving out forces loyal to the internationally recognized Palestinian Authority in 2007 and its rule has gone unchallenged through the blockade and four previous wars with Israel.

After breaking through Israeli barriers with explosives at daybreak Saturday, an estimated 1,000 Hamas gunmen rampaged for hours, gunning down civilians and snatching people in towns, along highways and at a techno music festival attended by thousands in the desert. Palestinian militants have also launched around 4,400 rockets at Israel, according to the military.

On Sunday, the U.S. dispatched an aircraft carrier strike group to the Eastern Mediterranean to be ready to assist Israel, and said it would send additional military aid.