An American-made, precision guided bomb that homes in on specific targets and, ideally, limits civilian casualties, was used in airstrikes in Gaza that killed dozens of Palestinians, including women and children.

The weapon, the GBU-39, or small-diameter bomb, was used in an attack at a former United Nations school on Thursday and in a May 26 strike in Rafah. In both cases, the Israeli military defended its actions, saying the strikes were aimed at militants using civilians as human shields. The Gaza health authorities said that civilians had also been killed, and there were videos and pictures of women and children among the dead.

Two weapons experts told The New York Times that Israel has appeared to increase the use of the bombs since the start of this year, compared with the war’s earliest days when it launched them in only 10 percent of airstrikes against Gaza. As a recent spate of Israeli strikes demonstrates, even a relatively diminutive bomb can inflict severe civilian casualties.

“The thing is, even using a smaller weapon, or using a precision guided weapon, doesn’t mean you don’t kill civilians, and it doesn’t mean that all of your strikes are suddenly lawful,” said Brian Castner, a weapons expert at Amnesty International.

Early in the war, the Israeli military mounted full-scale invasions of Gazan cities with tanks, artillery and 2,000-pound bombs, earning it international condemnation for heavy civilian casualties.