CAIRO (AP) — Human Rights Watch said Tuesday that Egypt’s security forces likely committed crimes against humanity when it crushed Islamist protests last year, comparing the bloodshed to China’s Tiananmen Square massacre and calling for a U.N. investigation into the role of President Abdel-Fattah el-Sissi, and his security chiefs.

In a 188-page report, the rights group accused security forces of deliberately using excessive force against supporters of Mohammed Morsi, the Islamist president ousted by el-Sissi last summer. It called the crushing of the main protester sit-in at Cairo’s Rabaah el-Adawiya Square on Aug. 14, 2013, the “world’s largest killings of demonstrators in a single day in recent history.”