More than 50 people were killed in Israeli air and ground attacks across the Gaza Strip on Sunday, according to local medics and rescuers.
They said children, a cameraman who worked for the Al Jazeera TV network and personnel from the Civil Defence agency were among the dead.
The Israeli military said it targeted sites used by Hamas and the allied armed group Palestinian Islamic Jihad.
The Hamas-run health ministry said the deaths meant the number of Palestinians killed in Gaza during the 14-month war between Israel and Hamas had surpassed 45,000.
The ministry does not make a distinction between combatants and civilians, but it reported in October that 29,980 children, women and elderly were among the identified fatalities.
The figures are often disputed by the Israeli government, which says almost 20,000 “terrorists” have been killed, but they are broadly accepted by UN agencies.
The war began when Hamas-led gunmen carried out an unprecedented attack on southern Israel on 7 October 2023, during which about 1,200 people were killed and 251 others were taken hostage.
Many of those killed on Sunday were in a UN-run school being used as a shelter for displaced families in the southern city of Khan Younis.
Harrowing footage showed a bloody scene on the third floor of Ahmed bin Abdul Aziz School, with children’s bodies apparently among those being removed.
“People were safe, staying in their homes after they prayed the dinner prayer. They were sitting, sleeping, and staying put in their places,” Manal Tafesh, whose brother and his children were among those killed, told Reuters news agency outside a local mortuary.
Medics said at least 13 people were killed, while a spokeswoman for the UN agency for Palestinian refugees (Unrwa) said she had heard reports of around 20 casualties, many of them women and children.
“It’s just doesn’t stop. It’s so relentless the pain and the suffering that we continue to have,” Louise Wateridge told the BBC from central Gaza.
The Israel Defense Forces (IDF) said it had “conducted a precise strike on Hamas terrorists who were operating inside a command-and-control centre” embedded within the school.
It also accused Hamas and other armed groups of exploiting civilians and using civilian infrastructure as human shields.
Medics said several more people were killed at another school-turned-shelter in the northern town of Beit Hanoun, which the UN said has been under siege by Israeli forces for more than two months.
The UN said it was monitoring reports that more than 1,500 people were newly displaced after Israeli forces besieged Khalil Aweida school and shelled it.
The IDF said on Sunday that its forces “conducted a targeted raid on a terrorist meeting point in the Beit Hanoun area”.
“In co-operation with the [Israeli Air Force], the troops struck dozens of terrorists from both the air and ground, and additional terrorists were apprehended,” it added.
Another strike hit a Civil Defence building in the urban Nuseirat refugee camp in central Gaza.
Civil Defence spokesman Mahmoud Basal said the strike killed the directors of its Nuseirat and Sheikh Radwan centres along with two volunteers, one of whom he named as Ahmad Baker al-Louh. Another five people were injured, three of them critically, he added.
“The Israeli occupation has once again shown the world that there is no protection for humanitarian workers in Gaza and no adherence to international humanitarian laws,” he said, adding that 94 Civil Defence workers had been killed since the start of the war.
Ahmad al-Louh was a cameraman for the Qatar-based Al Jazeera network, which strongly condemned what it called Israel’s “targeted killing” of its journalist.
It said Louh had been covering a rescue operation by the Civil Defence following an earlier strike on Sunday and that it came “just days after the targeting of his house”.
“The network calls on all human rights and media organisations to condemn the Israeli occupation’s systematic killing of journalists in cold blood, the evasion of responsibilities under international humanitarian law, and to bring the perpetrators of this heinous crime to justice,” a statement said.
The IDF said the Civil Defence building was used by “terrorists to plan and carry out an imminent terror attack against IDF troops”.
“Among the terrorists eliminated in the strike was the Islamic Jihad terrorist Ahmad Bakr al-Louh, who previously served as a platoon commander in the Islamic Jihad’s Central Camps Brigade,” it alleged, without providing any evidence.
Al Jazeera did not comment on the Israeli allegation, but Louh’s cousin Mahmoud told the Associated Press: “We were stunned by the Israeli occupation statement.”
“These claims are lies and misleading to cover up this crime,” he added.
The Committee to Protect Journalists says at least 137 journalists and media workers have been killed in Gaza, the occupied West Bank, Israel and Lebanon since the war began.