Israel is exerting control over a bigger slice of Gaza

Israel’s military has deepened its hold on the Gaza Strip, significantly expanding the territory it controls under the seven-month cease-fire and fortifying the line that separates it from areas controlled by Hamas.

Israel now holds around 59% of the enclave, up from 53% at the start of the U.S.-brokered cease-fire in October, people familiar with the matter said. The increase came as Israeli troops moved the so-called yellow line, which marks the division of territory, deeper into Hamas’s zone of control, the people said. In at least one spot, Israel moved the line forward a few hundred yards to intersect with Salah al-Din Road, Gaza’s main north-south artery.

In addition, in central Gaza, the Israeli military has been fortifying the line with a deep trench and high sand berms along its length, satellite images show. Similar earthworks can be seen in areas of northern and southern Gaza, but the fortifications through the center, where much of the population lives, are longer, more continuous and designed to be harder to breach since the area is more vulnerable to attack, Israel’s military says.

Satellite images show the line is now dotted with at least seven new outposts, each protected by sand berms. Some are paved with asphalt and host more than a dozen buildings. They beef up Israel’s position on the line and add to dozens of outposts scattered throughout its side of the enclave.

The fortifications show how the division of Gaza is hardening amid a logjam in President Trump’s peace process, as Hamas resists pressure to disarm its fighters and Israel continues to attack them. The situation means extended limbo for Palestinians who are still living among the ruins, and has created a no-man’s-land inside the enclave, a territory that Israel has long denied it wants to occupy permanently.

Scores of Gazans and at least five Israeli soldiers have been killed along the yellow line since the cease-fire. Israel says it has fired upon militants attacking its troops or on people who acted suspiciously around the dividing line. Palestinians say some civilians who didn’t know where the line was unwittingly came too close.

As long as Hamas remains in control of part of Gaza, Israel insists it won’t withdraw its troops, and many Arab governments say they won’t fund reconstruction of the enclave. The U.S.-led Board of Peace is pushing to get on with the task of reconstruction, including erecting new housing developments on the Israeli side of the line for Palestinians—a step some Arab governments as well as Hamas are resisting, according to Nickolay Mladenov, the diplomat leading the Trump-brokered effort to end the conflict.

“The more we stabilize the status quo, the more that status quo becomes difficult to remove,” Mladenov said in mid-May, warning of a situation in which Gaza becomes permanently split in two.

Asked about the movement of the yellow line, Israel’s military said it was operating on orders from the country’s political leadership. The office of Israeli Prime Minister Benjamin Netanyahu didn’t respond to a request for comment.

Hamas, in a statement earlier this month, said the line’s movement was evidence of the Israeli government’s “disregard of the mediators’ efforts” and its intention to renege on the agreement.

A Board of Peace official, when asked about Israel’s expansion of the yellow line, said the organization expects all sides to keep their commitments under Trump’s cease-fire plan, including Israel. The official added that the fastest way to achieve the aims of the cease-fire is for Hamas to agree to the sequencing road map laid out by Mladenov, which calls for a gradual disarmament of the group followed by a gradual Israeli withdrawal.

Netanyahu said this month that Israel now controls 60% of Gaza. That is in line with estimates made by the Civil-Military Coordination Center, which the U.S. set up in Israel to monitor the cease-fire and coordinate aid to the enclave, the people familiar with the matter said.

A White House official said there had been tremendous progress in implementing Trump’s peace plan.

The Trump administration strong-armed Israel and Hamas to accept a multistage peace deal last fall that began with a cease-fire and envisaged the disarmament of Hamas, the installation of a new government and security forces in Gaza, and the further withdrawal of Israeli troops. But progress has stalled at the cease-fire.

Israel has drawn up plans for a new round of fighting in Gaza that some officials say should begin after the war with Iran ends. That could involve raids and targeted killings as Israel gradually takes more territory from Hamas, said Ofer Guterman, a senior researcher at the Tel Aviv-based Institute for National Security Studies.

The militant group is focusing on rebuilding the military capabilities it lost during the war, including parts of its damaged tunnel infrastructure, Arab and Israeli officials have said.

“Israel, it seems, doesn’t really believe in the possibility the Trump plan will be implemented and Hamas disarmed, so we’ve improved our defensive posture in Gaza and are trying to improve the circumstances to resume the fighting,” Guterman said.

The growing barrier is to prevent vehicles from accessing the area around the yellow line, the Israeli military said. The decision to build it followed an incident in which an armed militant drove close to Israeli troops and fired at them near the yellow line, the military said.

The new outposts in Gaza facilitate the long-term deployment of troops but could be removed quickly if the government orders it, an Israeli military spokesman said. After the cease-fire, Israel swiftly left the military outposts along a corridor it carved across the center of Gaza.

The Israeli military installed yellow-painted concrete blocks to mark the border between the area under its control and the part controlled by Hamas after a handful of incidents at the outset of the cease-fire in which Palestinians were shot by Israeli troops while approaching the dividing line. The barrier along the yellow line will make it clearer to Gazan civilians where Israeli-controlled territory begins, the military spokesman said.

In mid-December, Israel moved the yellow blocks directly onto Salah al-Din Road and razed buildings on its side of the line.

Satellite images also show Israel has continued to raze buildings within the areas of Gaza it controls. The military said it is taking down buildings that were made uninhabitable during the war to enable reconstruction, as well as destroying structures that could pose a threat to nearby Israeli communities bordering Gaza.

In March, Israel sent aid groups in Gaza a map revising another boundary it calls the “orange line,” which runs parallel to the yellow line but deeper in Hamas-controlled territory, where most Gazans live. The military told aid groups they should coordinate with Israel for their safety before crossing that line.

Israel has been searching for tunnels crossing between the Hamas and Israeli areas of control by drilling all along the yellow line. Since the cease-fire, Israel has destroyed dozens of miles of tunnels located near the yellow line, according to Israeli military statements and videos.

Nearly all of Gaza’s two million residents are living in the Hamas-controlled areas, where humanitarian conditions continue to be difficult. Many in Gaza are still living in tents. The enclave has been struck with a severe rat infestation fueled by uncollected trash and warmer weather.

Meanwhile, Hamas has been reconsolidating its power over Gaza’s population and rebuilding the battered ranks of its armed wing, Mladenov and Israeli officials said.

Mladenov said Hamas is blocking efforts to build new temporary communities for displaced Palestinians within Israel-controlled territory. Hamas has rejected the allegation.

The situation in Gaza has been paralyzed by a lack of international pressure to push the parties to meet their obligations, said Ghaith al-Omari, a former official in the Palestinian Authority now at the Washington Institute.

“When diplomacy is not moving forward, the field starts dictating where we are going,” al-Omari said.

Write to Dov Lieber at dov.lieber@wsj.com and Emma Brown at Emma.Brown@wsj.com