Israeli strikes have killed at least 40 people who took refuge inside a UN school in the Gaza Strip, medics have said.
The strike on Tuesday hit a school run by the UN agency for Palestinian refugees, Unrwa, in the northern town of Jabaliya.
Medical sources at two Gaza hospitals said two tank shells exploded outside the school, where hundreds of Palestinians had sought refuge from the Israeli attacks.
The toll quickly rose as rescuers struggled through the rubble.
In addition to the dead, several dozen people were wounded, the officials said.
Doctors said all the dead were either people sheltering in the school or residents of Jabalya refugee camp, in the north of the Gaza Strip.
John Ging, director of operations in Gaza for Unrwa, the United Nations Relief and Works Agency, said three artillery shells landed near the school where 350 people were taking shelter.
Ging said Unrwa regularly provided the Israeli army with exact geographical coordinates of its facilities and the school was in a built-up area.
"Of course it was entirely inevitable if artillery shells landed in that area there would be a high number of casualties," he said.
"The initial findings... are that there was hostile fire at one of our units from the UN facility," Mark Regev, spokesman for the Israeli prime minister, said.
"Our unit responded. Then there were explosions out of proportion to the ordnance we used," he said.
Avital Liebowitz, an Israeli military spokesperson, told Al Jazeera that Hamas had "booby-trapped" installations in Gaza and Israel had no choice but to retaliate.
"This is how it is in wars, we did not choose to be in a war. However, Hamas chose to target Israelis, we did not force them to do anything, and Hamas chose terror."
But Azmi Bishara, a former Arab member of the Israeli Knesst, told Al Jazeera that Hamas' rockets were a "protest shout" against a "an occupying power".
"They are weapons of the poor, used to express their will.
"Israel would say, "what would any normal country do if they were threatened by rocket fire? They would act".
"But Israel is not a normal country, it is an occupying country, a colonial country and the people of Gaza are under siege."
Earlier in the day, two people were killed when an artillery shell hit a school in the southern town of Khan Yunis and three people were killed in an air strike on a school in the Shati refugee camp in Gaza City, medics said.
More than 640 people have been killed and 2,800 others wounded in the 11-day operation, most of them civilians
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