With international condemnation mounting, Prime Minister Benjamin Netanyahu of Israel said on Monday that the killing of dozens of people a day earlier at a camp for displaced Palestinians in Rafah was “a tragic accident,” but gave no sign of curbing the Israeli offensive in the southern Gaza city.

The deadly fire that tore through the encampment on Sunday after an airstrike came at a particularly delicate time for Israel, just days after the International Court of Justice appeared to order the country’s military to halt its offensive in Rafah and as diplomats were aiming to restart negotiations for a cease-fire deal between Israel and Hamas.

The Israel military said that the target of the strike in Rafah on Sunday was a Hamas compound, and that “precise munitions” had been used to target a commander and another senior militant official there.

But at least 45 people, including children, were killed by the blast and by the fires it set off, according to the Gaza health ministry. The ministry said that 249 people were wounded.

In a speech to the Israeli Parliament on Monday, Mr. Netanyahu said the military had sought to protect noncombatants, by issuing evacuation orders, adding that about a million civilians had left Rafah ahead of, or during, the offensive. “Despite our supreme effort not to harm uninvolved civilians,” he said, “a tragic accident occurred to our regret last night.”