A Gaza hospital said at least 37 people were killed on Thursday in an Israeli attack on a UN-run school that the Israeli military has accused of housing a “Hamas compound”.

The attack came as the military said it was launching new air and ground operations in central Gaza and an international medical group reported a sharp rise in casualties. The latest campaign appears to be an extension of Israel’s nearly eight-month offensive launched after Hamas’s October 7 attack.

At least 30 bodies were found at the Al-Aqsa Martyrs Hospital in Deir al-Balah from the attack on the school and six more from a separate attack on a house, according to hospital records and an Associated Press reporter at the hospital. Hamas-run media had earlier reported a higher death toll from the attack on the school.

The Israeli military said its warplanes struck a school run by the United Nations agency for Palestinian refugees, known as UNRWA. The Israeli military claimed, without immediately offering evidence, that Hamas and Islamic Jihad used the school as a cover for their operations.

The United Nations Refugee Agency (UNRWA) schools in Gaza have served as shelters since the start of the war, which has displaced most of the territory’s 2.3 million Palestinian population.

“Prior to the attack, a number of steps were taken to minimize the risk of harm to non-engaged civilians during the attack, including aerial surveillance and additional intelligence gathering,” the Israeli military said.

Both attacks took place in Nuseirat, one of several refugee camps built in Gaza, whose history dates back to the 1948 war, when millions of Palestinians fled or were expelled from their homes when Israel was created.

The latest war began with an Oct. 7 attack by Hamas on Israel, in which the militants killed about 1,200 people and took 250 others hostage. At least 36,000 Palestinians have been killed in Israeli attacks, according to Gaza’s health ministry, which does not distinguish between combatants and civilians in its figures.

The United States has voiced its support for a phased ceasefire and hostage release outlined by President Joe Biden last week. But Israel says it will not end the war without destroying Hamas, while the militant group is demanding a permanent ceasefire and a full withdrawal of Israeli forces.

The army said on Wednesday that troops were operating “both above and below ground” in eastern parts of Deir al-Balah and the Bureij refugee camp in central Gaza. It said the operation began with air strikes on militant infrastructure, after which troops launched “targeted daylight operations” in both areas.

Doctors Without Borders said at least 70 bodies and 300 wounded people, mostly women and children, were brought to a hospital in central Gaza on Tuesday and Wednesday following Israeli attacks.

The international charity said in a post on X on Wednesday that Al-Aqsa Martyrs Hospital is “struggling to treat the large number of patients, many of whom are arriving with severe burns, shrapnel wounds, fractures and other traumatic injuries.”

Gaza’s health system has been nearly collapsed by nearly eight months of war. The hospital, which was treating about 700 wounded and sick people before the latest attacks, said on Wednesday that one of its two electrical generators had stopped working, threatening its ability to run ventilators and incubators for premature babies.

Since the start of the war Israel has carried out regular air strikes on all parts of Gaza and launched a large-scale ground operation on the territory’s two largest cities, Gaza City and Khan Yunis, leaving most of them in ruins.

Earlier this year, the army launched a weeks-long offensive against Bureij and other refugee camps in central Gaza.

Troops withdrew from the Jabalia camp in northern Gaza last Friday after weeks of fighting left widespread destruction. First responders have recovered the bodies of 360 people killed during the fighting, most of them women and children.

Last month Israel sent troops into Rafah in what it described as a limited incursion, but those forces are now operating in central parts of Gaza’s southernmost city. More than 1 million people have fled Rafah since the operation began, many heading to central Gaza.