Israeli airstrikes early on Tuesday slammed into a part of the Gaza Strip that Israel had declared a humanitarian zone, killing at least 19 people and wounding 60, according to Gazan officials, in an area where tens of thousands of Palestinians forced from their homes had sought refuge in tents and makeshift shelters.

The Israeli military said in a statement that the strikes in Al-Mawasi, a coastal area of southern Gaza that was sparsely populated before the war, had targeted three senior Hamas militants who had been involved in the Oct. 7 Hamas-led assault on Israel.

Gaza’s Health Ministry said that the death toll was likely to rise as rescuers dug frantically through debris and sand for people who were reported missing, while ambulances struggled to reach the site. Health officials in Gaza do not distinguish between civilians and combatants when reporting casualties.

On a separate matter, Secretary of State Antony J. Blinken rebuked Israel over the fatal shooting last week of an American activist in the occupied West Bank, after the Israeli military acknowledged that one of its soldiers had probably killed her unintentionally. Israeli security forces “need to make some fundamental changes to the way they operate,” Mr. Blinken said.

Videos of the aftermath of the Al-Mawasi bombing, verified by The New York Times, show craters where satellite imagery from a week earlier showed several tents, with furniture, clothes and other belongings strewed across a wide area. People used their bare hands to dig through the sandy soil and move wreckage in search of victims in the predawn darkness, working by the lights of their phones, as emergency workers from the Palestine Red Crescent Society began digging with shovels.

Palestinians sheltering in Al-Mawasi said the strike came without warning around midnight or 1 a.m., with large explosions jolting their tents and filling them with smoke.