A day after Israeli forces bombed a United Nations school complex in central Gaza Strip that had become a shelter for displaced Palestinians, some of the facts remain unclear or under contention.

Israel said that it struck three classrooms used by 20 to 30 Palestinian militants, including some who participated in the October 7 Hamas-led attack on Israel, and that it was unaware of civilian casualties. Gaza health authorities said that among the dozens of people killed, many were children and women. Here is what we know and do not know.

What was bombed?

The multistory building was one of several that made up the UNRWA Nuseirat Boys’ Preparatory School. It was one of the many schools in Gaza run by UNRWA, the main UN agency for Palestinian refugees and their descendants.

Like all of the territory’s schools, it stopped operating as a school after the October 7 assault and Israel began its retaliatory bombing campaign. And like many of them, it became crowded with people who, displaced by the Israel-Hamas war from homes in other parts of Gaza, sought shelter in schools, hospitals and other institutions they hoped would be less likely to be bombed.

Philippe Lazzarini, director of UNRWA, said 6,000 people had been living in the school. About three-quarters of Gaza’s roughly 2.2 million people have fled their homes, many of them multiple times.

The Israeli military has referred to the school in Nuseirat as a militant base, saying that fighters for Hamas and Palestinian Islamic Jihad used three of its classrooms to plan and conduct operations against Israel.

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How many were killed in Nuseirat, and who were they?

The Israeli military on Friday released the names of eight Hamas and Palestinian Islamic Jihad fighters that it said were killed in the strike, adding to a list released Thursday and bringing the total to 17.

A military spokesperson, Lt. Col. Peter Lerner, said Thursday that he was “not aware of any civilian casualties” as a result of the strike. The military did not respond when asked whether that was still the case Friday.

But witnesses, medical personnel and Gaza officials said that dozens of civilians were killed — and that many were children or women.

A Gaza Health Ministry official Thursday said that at least 41 people were killed, and another said 46. Yasser Khattab, an official overseeing the morgue at Al-Aqsa Martyrs Hospital in nearby Deir al-Balah — where many of the bodies were taken — said There were 46 dead, including 18 children and nine women. But his statements could not be independently confirmed.

Khattab said the hospital had a well-practiced system for documenting and identifying bodies and parts of bodies. “We look for any marker that would help us identify the person,” he said.

A New York Times reporter who went to the hospital after the bombing saw it crowded with the bodies of the dead, the living and relatives of both, as well as medics trying to make their way through the mass of people. Witnesses described pulling the remains of children from the rubble at the school.

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Karin Huster, a medical coordinator with the aid group Doctors Without Borders who has been working at the hospital, said most of the patients she had seen in the past few days were women and children.

How careful was Israel’s action?

The bombing in Nuseirat exemplifies the awful calculus of the 8-month-old war. Operating within densely packed neighborhoods, Hamas is accused of cynically using Palestinians and civilian infrastructure as shields. In taking aim at Hamas, Israel regularly kills civilians and is accused — even by its allies — of using excessive, indiscriminate force.

The Israeli military maintains the airstrike was planned and carried out with care and precision, targeting only the three rooms in the school used by militants. Both there and at a camp in Rafah — where an Israeli bombing and subsequent fire killed 45 people in late May, according to Gaza officials — Israel used American-made GBU-39 bombs with about 37 pounds of explosive, which the military says are the carry the smallest of its warplanes.

The military said 20 to 30 Hamas militants had used the school as a base, including some who participated in the Oct. 7 assault. It said it had kept them under surveillance for three days before striking at the moment that would yield the fewest civilian casualties.

International laws of war prohibit using sites such as hospitals, schools and houses of worship for military purposes. Those laws also prohibit military forces from attacking such sites, with a limited exception if the enemy is using them.

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Israel says it operates within the bounds of that exception, because Hamas routinely operates within those buildings and in tunnels below them, making civilian casualties inevitable.

“We’re seeing that Hamas still exists, and they still have capabilities above and beneath the ground,” Lerner said Thursday.

In recent months, Israeli forces have repeatedly returned to places such as Nuseirat where they had previously seized control and then moved on, as Hamas fighters reappear there. Israeli officials have said that proves the need to carry out strikes such as the one Thursday.

How far an attacking force can go with such operations, legal experts say, differs case by case based on how it tries to safeguard civilians and distinguish them from combatants, and how proportional the attack is to the military advantage gained. In other words, it can be very murky in specific instances.