An Israeli airstrike on a school functioning as a shelter in Gaza City killed at least 30 people and injured dozens more on Sunday, according to the Palestinian emergency response agency in Gaza and Palestinian news outlets. It was the third attack on a school in the last four days.

Most of the victims were women and children, said Mahmoud Basal, a spokesman for the Palestinian Civil Defense. He said that an F-16 fighter jet hit a school called Hassan Salame, where at least 14 people were still buried under the rubble. Shrapnel and debris also hit a neighboring school known as Nasser, he said. The death toll was initially 25, but rose to 30.

It was unclear if any of those killed were militants.

The Israeli military said it had targeted “terrorists” in “Hamas command and control centers” located at the Hassan Salame and Nasser schools. It said it had taken “numerous steps to mitigate the risk of harming civilians” before the strike, including using precision munitions, surveillance and intelligence, though it did not specify how it had done so.

But civilians paid dearly.

“Right in front of me, there was a 5-year-old child dying. How is that related to Oct. 7?” Mr. Basal said. “If you want to kill someone, kill him away from other people.”

Sunday’s attack was a replay of similar scenes on Saturday at Hamama School, where Mr. Basal said 17 were killed in an attack, and on Thursday at Dalal al-Mughrabi School, where a strike killed 15, he said.

All four schools had housed Gazans who were forced to leave their homes during the war, turning classrooms and hallways into squalid temporary shelters. After each strike, videos on social media showed structures on fire, people screaming or running in shock and confusion and others lying motionless on the ground.