Dozens of people were killed by an overnight Israeli airstrike on a United Nations-run school in central Gaza, authorities said, in an attack that CNN analysis found was conducted with a US-made weapon.

The school, run by the UN agency for Palestinian refugees (UNRWA), was housing displaced people in the Nuseirat refugee camp at the time of the incident, the Gaza government media office said.

At least 45 people were killed in the strike, a spokesperson from Gaza’s Ministry of Health told CNN. Authorities at the nearby Al-Aqsa Martyrs Hospital said casualties could rise as victims were still being brought to the hospital on Thursday morning.

The Israeli military confirmed it carried out the airstrike, which it said targeted a Hamas compound operating inside the school. Israeli military spokesperson Lt. Col. Peter Lerner later told journalists the military was not “aware of any civilian casualties.”

Lerner said “20 to 30 Hamas and Islamic Jihad” militants were targeted in the strike, and that those targeted were “using the facilities to plan and execute attacks” against Israeli forces. Militants who were involved in the October 7 attacks on Israel were among those killed, Lerner said. CNN cannot independently verify any of those claims.

A CNN analysis of video from the scene and a review by an explosive weapons expert found that US-made munitions were used in the strike on the school. CNN identified fragments of at least two US-made GBU-39 small diameter bombs (SDB) in video filmed at the scene by a journalist working for CNN.

It marks the second time in two weeks that CNN has been able to verify the use of US-manufactured munitions in deadly Israeli attacks on displaced Palestinians, the first being a deadly IDF strike on a displacement camp in Rafah on May 26.

Thursday’s attack came after the IDF ramped up ground and air assaults in the center of the strip on Tuesday amid a deepening humanitarian crisis there. Palestinians in central Gaza have reported that the intensity and frequency of Israeli strikes in the last week have felt like the beginning of the war.

According to a journalist in the area working with CNN, the school was hit by at least three missiles that penetrated the three-story building. The facility was believed to be housing approximately 20,000 displaced people who had taken shelter in the school, its yard, and the surrounding area, according to the journalist.

“We were asleep here, (and) we suddenly saw rockets falling. I went down holding my child, we were both injured, my relative was martyred in that room,” Jaber Abu Daher told CNN on Thursday.

He said Israeli Prime Minister Benjamin Netanyahu “is killing the civilians, he is not killing militants, it’s innocent people asleep in a UNRWA facility… what did children and elderly do? What did they do to him? He is looking for Hamas people? Go look for them, why are you killing us in schools?”

US-made weapon used

Gaza authorities said the dead and injured continue to be brought to Al-Aqsa Martyrs Hospital, which is operating at three times its clinical capacity, “signaling a real disaster that will lead to a greater increase in the number of martyrs,” the Gaza media office said.

UNRWA said its school was “possibly hit several times” overnight by the strikes. An UNRWA spokesperson told CNN it was not able to confirm Israeli reports that Hamas operatives had been using the school as a compound.

“We remind all parties to the conflict that schools and other UN premises must never be used for military or fighting purposes,” the spokesperson said. “UN facilities must be protected at all times.”

Munitions made in the US were also used in the deadly Israeli strike on a displacement camp in Rafah late last month, a CNN analysis of video from the scene and a review by explosive weapons experts found.

After that attack, US President Joe Biden refused calls to alter his policy towards Israel, suggesting the deadly Rafah strike had not yet crossed a red line that would force changes in American support. He had previously said in a CNN interview that he wouldn’t allow certain US weapons to be used in a major offensive in Rafah.

In April, CNN reported that the Biden administration authorized the transfer to Israel of over 1,000 small-diameter bombs, according to three people familiar with the matter.

‘The situation is apocalyptic’

An Israeli strike hit the same camp last month and killed dozens of people, Al-Aqsa Martyrs hospital said at the time. One woman, Um Mohammad Taha, told CNN then that five houses had collapsed, including her sister’s, and that many were buried under the rubble, including children.

And another Israeli attack on the Nuseirat camp in April injured several journalists, including one working with CNN.

Doctors Without Borders/Médecins Sans Frontières (MSF), which has supported Al-Aqsa hospital, said Wednesday it had taken in more than 70 people who had been killed, and more than 300 injured, in just 48 hours, amid an escalation in bombing and ground fighting.

Karin Huster, an MSF nurse, said in the group’s statement: “We have seen hospitals being bombed. We have seen refugee camps being bombed. We have seen humanitarian warehouses being bombed. The situation is apocalyptic.”

“The odor of blood when I entered the emergency room was just overwhelming. People are lying on the floor. People are lying outside,” Huster added. “It’s just an emotionally overwhelming situation.”

Israel’s renewed focus on bombarding central Gaza highlights again the elusive nature of its stated ambition to destroy Hamas. The brunt of the Israeli military campaign had, in recent months, moved south towards Rafah, but rocket fire and ground warfare have now again engulfed encampments further north such as Nuseirat and areas like Bureij, both just south of Gaza City.

“Every place we went to after they said it’s safe was struck – I want the war to stop,” Mohammad Farajallah, a child who said his two brothers were killed in Thursday’s strike, told CNN as he rifled through the rubble of the school.

The latest attack also came as American, Egyptian and Qatari officials met in Doha to revive negotiations on a new ceasefire and hostage release deal.

The meetings follow a three-phase proposal — characterized as an Israeli plan — laid out by US President Joe Biden that would pair a release of hostages with a “full and complete ceasefire” in Gaza.

On Wednesday, Israel’s Minister of Defense Yoav Gallant said the country’s military offensive in Gaza would not be halted for any resumption of ceasefire and hostage release talks with Hamas.

“We are in a process of continuous engagement to wear down the enemy. Any negotiations with the terrorist organization Hamas will only be conducted under fire,” Gallant said in a recorded video statement.

This breaking news story will be updated. Journalist Mohammad Sawalhi contributed reporting from Gaza.