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 cease-fire on Aug. 26.

"Three Israeli attacks that damaged Gaza schools housing displaced people caused numerous civilian casualties in violation of the laws of war," it said in the report, based on interviews with witnesses and field research in the Hamas Islamist-dominated enclave.