Hala Khattab’s home in the city of Deir al-Balah in Gaza had been full of children — six of them. There was her oldest son, Hussein, 15; her 9-year-od quadruplets, Kinan, Hamman, Lujain and Sibal; and her baby girl, Wakeen.

Early on Sunday, an Israeli airstrike demolished the family’s second-floor apartment, killing Ms. Khattab, a 36-year-old teacher, and all her children, her family said. Their father, Ashraf Attar, narrowly escaped with his life.

“We collected the scattered body parts of the children,” said Ms. Khattab’s brother, Ahmad Khattab, a nurse who lives nearby and helped search the rubble. Mr. Khattab added, “There is absolutely no explanation” for the strike on the family.

The Israeli military confirmed an attack in Deir al-Balah on Sunday morning, saying that its air force had carried out a precision strike on “a significant Islamic Jihad terrorist” who had “directed attacks” on its troops throughout the war. The military said it had launched the strike after warning civilians on Friday to temporarily evacuate the area.

The military did not name the target of the strike, and it remained unclear if Israeli commanders believed he had lived in the Khattab family’s apartment or in another location.

The children’s father is also a nurse, not a militant, said Mr. Khattab 35. The strike demolished all the exterior walls of the family’s apartment in a three-story building, he said. The blast threw Mr. Attar from the apartment, leaving him with a broken arm and burned legs, the brother said.

The building is in an area that has never been ordered to evacuate during 10 months of war, and the family felt safe there, he said. The family did not receive an evacuation order or a warning call from the Israeli military just before the strike, either, Mr. Khattab said.

The strike came a day before Secretary of State Antony J. Blinken met with Prime Minister Benjamin Netanyahu in Israel at what Mr. Blinken called “a decisive moment” for diplomatic negotiations aimed at reaching a cease-fire deal between Israel and Hamas. The meeting came more than 10 months into a war that began when Hamas led an attack into southern Israel that killed about 1,200 people and led to the abduction of about 250 others into Gaza, Israeli officials said.

More than 40,000 Palestinians have also been killed in the war, according to Gazan health authorities, and it has taken an exceptional toll on children, who have been caught in the middle.

Dr. Khalil al-Dagran, the director of Al-Aqsa Hospital, said that his hospital received the bodies of Ms. Khattab and her six children on Sunday morning.

“What did these children do?” Mohammed Khattab, the children’s grandfather, said in a video interview with the Reuters news agency.

Ahmad Khattab said the family had buried the six children in one grave.