Fear plagued Saleh Mohammed al-Hila, 37, on that Sunday.

“I was lying on the ground of the tent and told my son ‘May God save us from this night,’” he recalled.

Hamas had launched rockets at central Israel hours earlier, setting off air-raid sirens in the Tel Aviv area for the first time in months. Israel’s military said the barrage had been fired from Rafah — the city in southern Gaza where Israeli forces were advancing and Mr. al-Hila was sheltering with his family in a camp for displaced people.

Israel was sure to retaliate, he thought. And it did — Israel’s military fired back and said it had destroyed the launcher used in the rocket volley, which was not near the camp.

But a few hours later, Israel struck again, dropping two 250-pound bombs on temporary structures in the camp. Lethal shrapnel hurtled in every direction and soon a fire was raging. By morning, dozens of Palestinians had been killed, including four of Mr. al-Hila’s relatives.

International outrage followed the second May 26 attack. Prime Minister Benjamin Netanyahu, who usually rejects criticism of Israel’s warfare, called the killing of civilians a “tragic accident.” Rear Adm. Daniel Hagari, the Israeli military spokesman, said there were “no tents in the immediate vicinity” of the targets. Israel said it had taken great care to avoid civilian harm, despite Hamas militants’ practice of operating among civilian centers, and that it would open an investigation into the strike.