KHAN YOUNIS, Gaza — The blast from the Israeli strike was so powerful that it threw an iron door clear over several neighboring houses. It came to rest along with a twisted laundry rack still laden Monday with singed clothes and a child’s slipper.

When the strike leveled a four-story house in the southern Gaza Strip the night before, it also killed four family households — 25 people, including 19 children — gathered to break the daily Ramadan fast together. Relatives said it also killed a guest of the family, identified by an Israeli human-rights group as a member of the Hamas military wing, ostensibly Israel’s target.

While Israel has said that its offensive is meant to stop extremist rocket fire and destroy Hamas’ secret tunnel network, the attack Sunday night was the latest in a series of Israeli bombings that have killed families in their homes.

Israel has insisted that the civilians are dying because Hamas has cynically chosen to operate among them, using them as shields.

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But while Israel has, in the past, killed Hamas members with attacks so precise that others riding in their cars have survived, in this conflict, there have been numerous instances of family homes being struck with residents inside. More and more Palestinians are accusing Israel of trying to inflict maximum suffering to demoralize Palestinians and weaken support for Hamas.

On July 13, 18 family members were killed in an airstrike on their home, including Tayseer al-Batsh, the Hamas police chief in Gaza. Many other civilians have been killed in strikes on known Hamas offices or apartments that happened to be in their apartment buildings, and in strikes on homes with no obvious connection, Palestinian officials and residents say.

On Monday night, a strike hit an eight-story apartment building in downtown Gaza City — an area where Israeli officials had urged Gazans to take shelter. The building collapsed as rescue crews were inside, killing more people. The death toll, at least 13, was still being tallied.

Speaking in general, a senior Israeli military official said that not all civilian casualties come from strikes going astray; some take place when civilians are in places the military aims to hit.

“Not all the casualties are due to mistakes,” he said. “If Hamas are holding people inside the apartments while shooting from there, that’s one of the tragedies they are making.”

That did not appear to be the situation at the Abu Jameh home, where, survivors said, the family was gathered to break its daily Ramadan fast, a ceremonial meal, a time when Israeli military officials would have known that people were likely to be home.

All the dead were from the Abu Jameh family, according to relatives, except for a guest, whom the Israeli rights group, B’Tselem, identified as Ahmad Suliman Sahmoud, a member of Hamas’ military wing, who was visiting a member of the family.

Family members said that no one in the house was a Hamas fighter, although they said that one resident, Tawfik Abu Jameh, was a bodyguard for an official in charge of Gaza’s border crossings. He escaped the bombing, having gone to pray, but lost his wife and all but one of his children.

Some members of Gaza’s security forces are former members of Hamas’ extremist Qassam brigades. Bassem Naim, who served as health minister in a former Hamas government in Gaza, noted Monday that the international community had encouraged extremists to become part of the official security forces, with the idea that it would moderate some. Now, he said, if former Hamas fighters can be targeted when they are in their homes with families, then so can the majority of Israeli adults who are army reservists.

While not everyone in Gaza supports Hamas — the territory has been perennially rived by factional disputes with Fatah, a faction more disposed toward negotiation with Israel — the group is deeply embedded in Gazan society. Those considered its members range from fighters in the Qassam Brigades to members of the political wing, government workers or police.