Deadly Gaza strike raises US concerns about civilians, despite precision munitions

An Israeli attack on a UN school complex in central Gaza is raising alarm among U.S. officials after scores of civilians were reportedly killed, despite the apparent use of American-made precision munitions.

The Hamas-run Gaza Ministry of Health said Thursday's airstrike on the school, which has become a makeshift shelter for thousands of displaced people inside the enclave, left at least 40 people dead, including more than a dozen children.

State Department spokesperson Matthew Miller said U.S. officials were in direct contact with the Israeli government about the strike, and its claim its forces were targeting "20 to 30 members of Hamas and other militant groups" and used a "precision strike to target only one part of the building without hitting areas where civilians were sheltering."

But Miller expressed concern about the children reportedly among the dead.

"Certainly, if that it is accurate that 14 children were killed -- those aren't terrorists. And so the government of Israel has said that they're going to release more information about this strike, including the names of those who died in it," Miller said. "We expect them to be fully transparent in making that information public."

In late May, another Israeli airstrike on two Hamas targets in Rafah sparked a fire that Gazan authorities say killed at least 45 Palestinians sheltering in a nearby encampment, marking the deadliest incident of Israel's offensive on the enclave's southernmost city.

In both that attack and Thursday's strike on the school, weapons experts tell ABC News that fragments at the sites indicate that American-supplied munitions -- GBU-39 small diameter bombs -- were used.

Although these explosives are designed to have a more limited impact that other arms provided to Israel by the U.S., experts say small diameter munitions can still have a devastating and unpredictable impact in a densely populated area.

A spokesperson for the Israeli military, Daniel Hagari, said the strike in the early hours of Thursday was based on "concrete intelligence" that indicated that militants inside the school were involved in carrying out the Oct. 7 Hamas attack on Israel and were "planning more attacks against Israelis, some of them imminent."

"We stopped a ticking time bomb," Hagari said.

Miller could not confirm whether American-made weapons were used in Thursday's attack but said that "on a number of occasions" U.S. officials had pressed Israel "to use the most precision weapon possible and the smallest weapon possible to achieve legitimate military gains."

"If it bears true that this strike resulted in the death of 14 children, the results aren't where they need to be," Miller said.

A spokesperson for United Nations Secretary-General António Guterres condemned the strike, saying in a statement "UN premises are inviolable, including during armed conflict and must be protected by all parties at all times."

Through the Israel-Hamas war, the Biden administration has acknowledged that civilian deaths are an unfortunate consequence of any armed conflict while maintaining that Israel has a right to defend itself, even in some instances involving targets like schools and hospitals that are also being used by combatants -- a grey area of international humanitarian law.

However, the Biden administration's view of what constitutes legitimate military gains may be shifting.

When the president announced the framework for cease-fire deal that would free the scores of hostages imprisoned inside Gaza, he also declared that Israel had degraded Hamas to the point that the militant group is "no longer capable of carrying out another Oct. 7."

U.S. officials maintain that Israel must retain the ability to address imminent threats, as the Israeli government asserts it did by striking the school. Through the conflict, Israel has not made a consistent practice of sharing intelligence justifying its attacks with its allies or the public.

Still, the Biden administration has generally defended Israel's strikes on civilian centers, noting that Hamas is known to use them as human shields for its fighters.

But Palestinians in Gaza say the end result is that they are left with no refuge from the horrors of war.

Muhammad Bahar, 42, says he was sleeping in the basement of a building in the school complex when it was hit by a missile overnight.

"I can't believe I'm still alive," he told ABC News as he stood beside the rubble.

"They said go to [United Nations Relief Works Agency] schools because they are safe. Since the beginning of the war we have been here," he said. "But this is what happened."

ABC News' Diaa Ostaz, Morgan Winsor, Helena Skinner and Chris Looft contributed to this report.