An Israeli strike on a school sheltering displaced Palestinians in central Gaza has killed more than 30 people including 23 women and children, according to health officials.

The Israeli military said Hamas militants were operating from the school in Nuseirat.

The strike on Thursday came after the military announced a new ground and air assault in several refugee camps in central Gaza, pursuing militants it says have regrouped there.

It is the latest instance of troops sweeping back into sections of the Gaza Strip they have previously invaded, underscoring the resilience of the militant group despite Israel’s nearly eight-month onslaught.

Witnesses and hospital officials said the pre-dawn strike hit the al-Sardi School, run by the United Nations agency for Palestinian refugees known as UNRWA. The school was filled with Palestinians who had fled Israeli offensives and bombardment in northern Gaza, they said.

Ayman Rashed, a man displaced from Gaza City who was sheltering at the school, said the missiles hit classrooms on the second and third floor where families were sheltering.

The Al-Aqsa Martyrs Hospital in the nearby town of Deir al-Balah received at least 33 dead from the strike, including 14 children and nine women, according to hospital records and an Associated Press reporter at the hospital.

Another strike on a house overnight killed six people, according to the records. Both strikes occurred in Nuseirat, one of several built-up refugee camps in Gaza dating to the 1948 war surrounding Israel’s creation, when hundreds of thousands of Palestinians fled or were driven from their homes in what became the new state.

Online footage showed bodies wrapped in blankets or plastic bags being laid out in lines in the courtyard of the hospital, which was largely dark as staff try to conserve limited fuel for electricity.

Mohammed al-Kareem, a displaced Palestinian sheltering near the hospital, said he saw people searching for their loved ones among the bodies, adding: “The situation is tragic.”

The Israeli military said Hamas had embedded a “compound” in the school and that Hamas and Islamic Jihad militants inside were using it as a shelter where they were planning attacks against Israeli troops.

It released a photo of the school, pointing to classrooms on the second and third floor where it claimed militants were located.

It said it took steps before the strike “to reduce the risk of harming uninvolved civilians… including conducting aerial surveillance, and additional intelligence information”.

UNRWA schools across Gaza have functioned as shelters since the start of the war, which has driven most of the territory’s population of 2.3 million Palestinians from their homes.

Israel launched its campaign in Gaza after Hamas’s October 7th attack into Israel, in which militants killed 1,200 people and took another 250 hostage.

Israel’s offensive has killed at least 36,000 Palestinians, according to Gaza’s Health Ministry, which does not distinguish between fighters and civilians in its figures.

Israel blames civilian deaths on Hamas because it positions fighters, tunnels and rocket launchers in residential areas.

The US has thrown its weight behind 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 lasting ceasefire and the full withdrawal of Israeli forces.

The military said on Wednesday that forces 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 began a “targeted daylight operation” in both areas.

Doctors Without Borders said at least 70 bodies and 300 wounded people, mostly women and children, were taken to a hospital in central Gaza on Tuesday and Wednesday after a wave of Israeli strikes.

The international charity said on Wednesday that Al-Aqsa Martyrs Hospital was struggling to treat “a huge influx of patients, many of them arriving with severe burns, shrapnel wounds, fractures, and other traumatic injuries”.