Israel Shifts to Tougher Phase of Its Gaza War

Israeli forces have largely succeeded in taking control of northern Gaza. But they have only partially destroyed Hamas’s military capabilities and haven’t captured or killed many of its top leaders, senior Israeli officers and analysts say.

Israeli commanders have signaled the shift to the south in recent days, suggesting that many Hamas fighters have escaped there as Israeli troops moved in and that some leaders are ensconced in densely populated towns, or in underground tunnels, that have seen fewer airstrikes and less fighting than Gaza City in the north.

Hamas will almost certainly prove to be a more determined adversary in the south, where the militants will have few remaining options other than to fight. The hostages are the best leverage Hamas leaders have for surviving the Israeli shift to the south, as the militants seek a halt to the fighting, at least temporarily, former Israeli officers say.

Israel’s plan for attacking Hamas in the south is likely to resemble its advance in the north, but it will be complicated by the large number of civilians now packed into the area, Israeli officials and commanders say.

“We are determined to keep moving forward," Rear Adm. Daniel Hagari, the Israeli military’s chief spokesman, said Friday. “This will happen wherever Hamas is, and it is also in the southern Gaza Strip."

U.S. officials say they are urging Israel to delay its stepped-up operations in the south until it has thought through plans for protecting civilians who have fled there in large numbers to escape the fighting in the north.

“We think that their operations should not go forward until those people—those additional civilians—have been accounted for in their military planning," Jonathan Finer, the U.S. deputy national security adviser, said Sunday on CBS’s Face the Nation. “We will be conveying that directly to them and have been conveying that directly to them."

Israel should narrow “the area of active combat, clarifying where civilians can seek refuge from the fighting" in the south, he added.

Israeli officials say they have no choice but to also invade the southern and central Gaza Strip to achieve the Israeli government’s aim of removing Hamas from power in response to the Oct. 7 cross-border attack that Israel says killed more than 1,200 people, including many civilians, and resulted in the kidnapping of some 240 others.

Nearly all of the roughly two million people who live in Gaza are now crowded into schools, refugee camps and homes in the south. Since Israel imposed a total siege on the territory in October, Palestinian civilians are increasingly desperate, with dwindling supplies of food, a lack of clean water, no electricity, and sewage overflowing in the streets. Rising Palestinian casualties, with more than 12,000 dead according to health authorities in Hamas-run Gaza, will only increase international pressure for a halt in the fighting.

One of Israel’s objectives in the south will be to block the border with Egypt, including tunnels underneath it, to prevent Hamas from bringing in more weapons to prolong the fight and to stop its leaders from escaping Gaza if the group’s fight continues to go poorly, analysts and Israeli security officials said.

“The main Hamas leaders have never been sitting in the north," said Miri Eisin, a former deputy head of the Israeli military’s combat intelligence corps. “They’re going to stay close to home and the bulk of them live in central and the south of Gaza."

Israel’s top targets are Yahya Sinwar, the most senior Hamas leader in Gaza, and Mohammed Deif, Hamas’s military commander whom Israel has accused of coordinating the Oct. 7 attacks.

Israeli warplanes are likely to intensify bombing of Khan Younis and Rafah, the south’s densely packed urban areas believed to be honeycombed with Hamas tunnels, like Gaza City in the north. That will likely be followed with ground troops advancing from multiple directions, isolating Hamas strongholds and slowly clearing them of fighters above ground.

“They will move slowly, slowly. First bombing from the air from the sea and from the land and then the infantry and the tanks," said Eyal Pinko, a retired Israeli military officer and former intelligence official.

In a sign of the intensifying focus on the south, an Israeli airstrike Saturday hit a housing development on the outskirts of Khan Younis, according to a spokesman for the Ministry of Health in Hamas-controlled Gaza. The attack killed 26 people and wounded another 20, the spokesman said.

An Israeli military spokesman said he couldn’t comment on the target of the attack. “The IDF follows international law and takes feasible precautions to mitigate civilian harm," the spokesman said.

Israeli troops have stayed out of the tunnels in the north, commanders say, opting to blow up the entrances in many cases when they find them to prevent Hamas from using them to mount ambushes. But as the search for hostages continues in the south, determining which tunnels can be destroyed without endangering hostages could prove increasingly difficult.

Lt. Col. Richard Hecht, a spokesman for the Israeli military, underscored the difficult tactical issues facing its commanders as they weigh the next steps in the south: “I can’t tell you what our operational plan is. We still haven’t decided it yet," he said Friday.

Palestinians who are now crammed into a smaller section of the enclave have no viable way of leaving. To the south, the Rafah border crossing with Egypt remains closed for all except those with special permits, usually people with foreign citizenship. To the north, Gaza City is now largely uninhabitable after more than a month of war and isolated from the rest of the strip by the Israeli army.

“Some of the challenges are going to remain the same in the south," said John Spencer, a retired U.S. Army officer and chair of urban warfare studies at the U.S. Military Academy. “But one of the differences is they have sent everybody down there, so they face an even more difficult situation separating civilians from Hamas."

Israel’s military estimated Friday it had killed around 1,000 Hamas fighters, a small portion of the force of more than 30,000 that it said were in the group’s ranks before the war.

“Take that with the hostage situation and mix that together. That’s a huge strategic operational tactical spaghetti," Spencer said.

Israeli warplanes in recent days have dropped leaflets in southern Gaza encouraging residents to flee to an even smaller area called al-Mawasi, a ribbon of farmland about half a mile wide and 9 miles long along the Mediterranean coastline. Israel says it wants to set up a safe “humanitarian zone" in the area, while U.N. officials have said the idea is unworkable.

Some Israeli military officials acknowledge that it would be impossible to corral two million Gaza residents into al-Mawasi, which is about the size of Los Angeles’ LAX airport. Still, the operation in the south will require displacing Palestinian civilians from individual towns and neighborhoods, Israeli officials say.

“What we’re going to do is a local evacuation for a short period of time," said reserve Maj. Gen. Tamir Hayman, the managing director of Israel’s Institute for National Security Studies. “Later on when we withdraw, we will bring them back. It’s very complicated. I know how it sounds and I know how it will look, but we have no alternative."

The current phase of Israel’s military operation, in northern Gaza, is expected to continue for weeks before the Israeli military turns to the south, according to a U.S. intelligence assessment described to The Wall Street Journal by a U.S. official. Israel hasn’t put a timeline on how the offensive will unfold.

Israel’s anticipated assault on southern Gaza will likely raise the pressure on Egypt to allow more Palestinian refugees to enter the country. Egypt has so far rejected the idea of accepting a large number of Palestinians on principle, calling it an attack on Palestinian territorial integrity. Egyptian officials also have security concerns about the potential for militants to enter the country.

Nasser Qassem, a 37-year-old father of three, fled his home in Gaza City and moved to the southern city of Khan Younis in search of safety. He said he feared the next phase of the Israeli operation would push Palestinians toward Egypt’s neighboring Sinai peninsula.

“I think this might be the first step of pushing us to Sinai, but I myself prefer to be killed here, I won’t end up in a tent in Sinai. I evacuated three times, but I’m not gonna leave the Gaza Strip no matter what," he said.

The leaders of U.N. humanitarian agencies and other major relief groups have rejected calls for the creation of a “humanitarian zone" or a “safe zone" in part of the southern Gaza Strip, arguing that civilians should be protected from attacks wherever they are. The U.N. also urged Israel to rescind its initial demand for Palestinians to leave northern Gaza, calling it an act of forced displacement.

“In our view it’s just a distraction from the obligations of the parties to the conflict to take care for civilians wherever they are and provide humanitarian access," said Sam Rose, director of planning at the U.N. Relief and Works Agency that serves Palestinian refugees.

In southern Gaza, where humanitarian agencies have had more access compared with the north, basic services such as running water, sewage and communications are breaking down.

“A population that was already starved of basic needs is now completely on its knees. We’re seeing the breakdown of basic needs even in the south," said Rose. “We were stretched beyond breaking point anyway. Things were already grinding to a halt. Things are going to get worse."

Abeer Ayyoub in Istanbul contributed to this article.

Write to David S. Cloud at david.cloud@wsj.com and Jared Malsin at jared.malsin@wsj.com