JERUSALEM (AP) — Twenty-one soldiers were killed in the Gaza Strip in the deadliest attack on Israel’s forces since the Oct. 7 Hamas raid that triggered the war, the military said Tuesday, a major setback that could add to mounting calls for a cease-fire.

The reservists were preparing explosives to demolish two buildings in central Gaza on Monday when a militant fired a rocket-propelled grenade at a tank nearby. The blast triggered the explosives, causing both two-story buildings to collapse on the soldiers inside.

Prime Minister Benjamin Netanyahu has vowed to press ahead until Israel crushes the ruling Hamas militant group and wins the freedom of over 100 hostages held captive in Gaza. But Israelis are increasingly divided on the question of whether it’s possible to do either, and large numbers of Israeli casualties have pressured Israel’s government to halt past military operations.

Defense Minister Yoav Gallant said it was a “difficult and painful morning,” but that Israel was still committed to pressing ahead. “This war will determine the future of Israel for decades to come, and the fall of soldiers is a requirement to achieve the goals of the war,” he wrote on X, formerly known as Twitter.

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Families of the hostages and many of their supporters have called for Israel to reach a cease-fire deal, saying that time is running out to bring the hostages home alive. On Monday, dozens of hostages’ relatives stormed a parliamentary committee meeting, demanding a deal to win their loved ones’ release.

Israel launched its offensive after Hamas’ Oct. 7 cross border attack that killed over 1,200 people and abducted some 250 others. More than 100 were released in November in exchange for a weeklong cease-fire and the release of 240 Palestinians imprisoned by Israel.

The offensive has caused widespread destruction, displaced an estimated 85% of Gaza’s population and left over 25,000 Palestinians dead, according to health officials in the Hamas-run territory. The United Nations and international aid agencies say the fighting has unleashed a humanitarian disaster, with a quarter of Gaza’s 2.3 million people facing starvation.

The war has heightened regional tensions, with Iran-backed groups in Lebanon, Syria, Iraq and Yemen attacking United States and Israeli targets in support of Palestinians. The U.S. and Britain launched another wave of strikes Monday against the Houthi rebels in Yemen, who have targeted international shipping in the Red Sea in what they portray as a blockade of Israel.

DEADLY FIGHTING IN THE CENTER AND SOUTH

Hamas is believed to have suffered heavy losses but has continued to put up stiff resistance in the face of one of the deadliest air and ground offensives in recent history. Militants are still battling Israeli forces across the territory and launching rockets into Israel.

The attack that killed the soldiers occurred some 600 meters (yards) from the border in Maghazi, one of three built-up refugee camps in central Gaza dating back to the 1948 war surrounding Israel’s creation.

Ground operations have been focused on the camps, as well as the southern city of Khan Younis, after Israel claimed to have largely defeated Hamas in northern Gaza in operations that caused widespread destruction to that part of the territory, including Gaza City.

Dozens of Palestinians were killed Monday in heavy fighting in Khan Younis, where people dug graves in the courtyard of the city’s Nasser Hospital as staff struggled to deal with the large number of wounded people, including children.

Gaza’s internet and phone networks collapsed again Monday for the 10th time during the war, posing another challenge for first responders and making it impossible for people to reach loved ones in different parts of the territory.

Israel believes Hamas commanders may be hiding in vast tunnel complexes beneath Khan Younis, the hometown of the group’s top leader in Gaza, Yehya Sinwar, whose location is unknown. Hamas leaders are also believed to be using hostages as human shields, further complicating any rescue efforts.

PRESSURE FOR A CEASE-FIRE

The growing death toll and dire humanitarian situation have led to increasing international pressure on Israel to scale back the offensive and agree to a pathway for the creation of a Palestinian state after the war. The United States, which has provided crucial military aid for the offensive, has joined those calls.

But Netanyahu, whose popularity has plummeted since Oct. 7 and whose governing coalition is beholden to far-right parties, has rebuffed both demands.

Instead, he has said Israel will need to expand operations and eventually take over the Gaza side of the border with Egypt, where hundreds of thousands of Palestinians who have fled from other areas are packed into overflowing U.N.-run shelters and sprawling tent camps.

That drew an angry protest from Egypt’s government, which rejected Israeli allegations that Hamas smuggles in weapons across the heavily-guarded frontier.

Diaa Rashwan, head of Egypt’s State Information Service, said Monday that any Israeli move to occupy the border area would “lead to a serious threat” to relations between the two countries, which signed a landmark peace treaty over four decades ago. Egypt is also deeply concerned about any potential influx of Palestinian refugees into its Sinai Peninsula.

Rashwan said Egypt was in full control of the border after taking a number of measures in recent years, including the creation of a 5-kilometer (3-mile) buffer zone and the construction of barriers above and below ground.

Egypt “is capable of defending its interests and sovereignty over its land and borders, and will not mortgage it in the hands of a group of extremist Israeli leaders who seek to drag the region into a state of conflict and instability,” Rashwan said.

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Jobain reported from Rafah, Gaza Strip. Associated Press writer Samy Magdy in Cairo contributed.