A United Nations aid agency car lies destroyed by shrapnel from an Israeli strike in the Jebaliya refugee camp, northern Gaza Strip, Tuesday, July 29, 2014.

Israel’s military attacks on United Nations schools in Gaza that were sheltering thousands of displaced people slaughtered dozens of civilians “in violation of the laws of war,” Human Rights Watch declared in a report released Thursday.

The humanitarian organization investigated three separate attacks on such schools that occurred in late July and early August, which together killed 45 people, 17 of them children. “Israel has offered no convincing explanation for these attacks on schools where people had gone for protection and the resulting carnage,” said Fred Abrahams, special adviser at Human Rights Watch.

On July 24, Israel shelled a UN elementary school in Beit Hanoun, killing 13 people, including six children, and wounding dozens, the report states. Fifty-eight-year-old witness Jamal Abu ‘Owda described to Human Rights Watch seeing, in the aftermath, “shredded bodies, a mix of everything, boys, men, girls, women, a mix of different faces and bodies.” Witnesses testify that at least four successive shells hit the school courtyard, in addition to more shelling just outside the compound, contradicting the Israeli military’s claim that “a single errant mortar” hit the “empty” courtyard, the report notes.

On July 30, another Israeli attack on a UN girls’ elementary school in Jabalya, which was sheltering over 3,200 people, killed 20 people, three of them children. “The Israeli military said that Palestinian fighters had fired mortars ‘from the vicinity’ of the school, but provided no information to support that claim,” notes the report. “In any event, the use of high-explosive, heavy-artillery shells so near a shelter filled with civilians constitutes an indiscriminate attack.”

On August 3, an Israeli missile struck immediately outside a UN boy’s school in Rafah, killing 12 people, 8 of them children, and wounding dozens. Offering no evidence, the Israeli military claimed the strike targeted Islamic Jihad members. But the report notes that Israeli military offered no explanation for “why it attacked the men in front of a school sheltering thousands of displaced people rather than before they arrived or after they drove away.”

While the Israeli military claims to have launched an investigation of itself to “examine exceptional incidents” during the bombardment of Gaza, the Human Rights Watch report notes, “Previous inquiries by the Israeli military of alleged war crimes committed by its forces have not met international standards for credible, impartial and independent investigations.” The report urges rigorous investigations of the assaults on UN schools and other Israeli attacks on civilians by the United Nations and the International Criminal Court.

In seven weeks of military bombardment on the besieged Gaza strip, commencing in early July, Israel killed at least 2,145 Palestinians, 578 of them children and 102 of them elderly, according to Gaza’s Health Ministry. Furthermore, Israel wounded at least 11, 100,  including 3,374 children. Officials of numerous international institutions and organizations, including the United Nations, have stated that Israel likely violated human rights law.