A trail of blood is seen in the courtyard of a UN School in the northern Beit Hanun district of the Gaza Strip on July 24.

GAZA — Human Rights Watch accused Israel of committing war crimes by attacking three U.N.-run schools in the Gaza Strip in fighting in July and August, killing Palestinian civilians who had sheltered there.

The New York-based group issued a report on Thursday that it described as the first in-depth documentation of the incidents, which took place during a 50-day conflict between Israel and Palestinian militants that ended in a ceasefire on Aug. 26.

“Three Israeli attacks that damaged Gaza schools housing displaced people caused numerous civilian casualties in violation of the laws of war,” the report stated, based on interviews with witnesses and field research in the enclave.

Israeli government and military spokesmen declined immediate comment. But during the Gaza fighting, Israel rejected preliminary Human Rights Watch findings it committed war crimes and said the group should focus on Hamas putting Palestinian civilians in harm’s way by using residential areas as launching points for attacks and for weapons storage.

On Thursday, Human Rights Watch also said it was skeptical about the credibility of five criminal investigations announced by Israel’s military on Wednesday into its Gaza war operations.

The organization said 45 people, including 17 children, were killed in or near the “well-marked schools” in the strikes on July 24 in the northern Gaza town of Beit Hanoun, on July 30 in Jabalya refugee camp and on Aug. 3 in Rafah, in the south of the enclave.

It said its inspection of the Beit Hanoun site and photographs of munitions remnants suggested Israel fired mortars at the school, killing 13 people.

The Israeli military said at the time the school was hit by errant fire and the area around the facility had been used by Palestinian fighters to launch rockets.

In the Jabalya attack, Human Rights Watch said, Israeli artillery shells killed 20 people at the school.

Twelve people were killed at the school in Rafah, Human Rights Watch said, and an impact crater and fragments “strongly suggested” a Spike missile had been fired by an Israeli aircraft. The military said shortly after the incident that it had targeted three militants on a motorcycle near the school.

Human Rights Watch, which called in its report for “all parties in the armed conflict in Gaza” to take measures to minimise harm to civilians, said the attacks on the Beit Hanoun and Jabalya schools “did not appear to target a military objective or were otherwise indiscriminate,” while the third strike, in Rafah, was “unlawfully disproportionate.”