The latest bloodshed came after Israel again warned civilians to relocate as it girds for an onslaught against Hamas in the enclave's south, after subduing the north.
"Receiving horrifying images & footage of scores of people killed and injured in another @UNRWA school sheltering thousands of displaced in the north of the Gaza Strip," UNRWA Commissioner-General Philippe Lazzarini said on social media platform X.
"These attacks cannot become commonplace, they must stop. A humanitarian ceasefire cannot wait any longer."
Israel's military did not immediately comment. A spokesperson for Gaza's Hamas authorities said 200 people had been killed or injured.
TVNL Comment: Goddam!!! The Israelis ordered citizens of northern Gaza to evacuate to the south where they would be safe. Then they attack the south, killing hundreds. This is a land grab to kill as many civilians as possible and steal their land. What a shock!!!