A United Nations inquiry has blamed the Israeli military for seven attacks on UN schools in Gaza that were used as shelters during the 2014 war.
"I deplore the fact that at least 44 Palestinians were killed as a result of Israeli actions and at least 227 injured at United Nations premises being used as emergency shelters," Secretary-General Ban Ki-moon said in a letter to the Security Council.
"It is a matter of the utmost gravity that those who looked to them for protection and who sought and were granted shelter there had their hopes and trust denied," Mr Ban added.
The UN chief vowed to "spare no effort to ensure that such incidents will never be repeated".
The board of inquiry investigated the attacks on the schools run by the UN Palestinian refugee agency UNRWA from 8 July to 26 August last year, but it also shed light on the discovery of weaponry at three schools.
The schools were vacant at the time but Mr Ban noted that "the fact that they were used by those involved in the fighting to store their weaponry and, in two cases, probably to fire from, is unacceptable".
Israel has repeatedly maintained that Hamas militants were using civilians as human shields and UN premises as storage sites for weapons during the 50-day war.
In response to the report, Israel's foreign ministry said criminal investigations have been launched against those linked to the attacks on shelters.
"Israel makes every effort to avoid harm to sensitive sites, in the face of terrorist groups who are committed not only to targeting Israeli civilians but also to using Palestinian civilians and UN facilities as shields for their terrorist activities," said foreign ministry spokesman Emmanuel Nahshon.
The Gaza war ended with a Egyptian-brokered truce after about 2,200 Palestinians, most of them civilians, and 73 Israelis, mostly soldiers, were killed.