Israeli strikes near a market in the eastern Gaza Strip killed 19 Palestinians on Wednesday, the local health ministry said.
Residents said that Israeli shelling and two missiles from the air hit the area in Shejaia, on the fringes of the city of Gaza. Ashraf al-Qidra, spokesman of the Gaza Health Ministry, said 160 people were also wounded.
An Israeli military spokeswoman said militants had fired mortar bombs from the vicinity of the school and troops shot back in response. The incident was still being reviewed.
The army said three Israeli soldiers were killed on Wednesday when a booby-trap bomb exploded in a tunnel shaft they had uncovered in a residence in the southern Gaza Strip.
UNRWA said on Tuesday it had found a cache of rockets concealed at another Gaza school – the third such discovery since the conflict began. It condemned unnamed militant groups for putting civilians at risk.
Krahenbuhl said the Jabalya school’s precise location and the fact that it was sheltering thousands of displaced people had been communicated to the Israeli military 17 times, with the last notification just hours before the fatal shelling.