The Israeli assault on Gaza has seen its bloodiest day so far, bringing the Palestinian death toll to more than 500. More than 100 Palestinians were killed in a 24-hour period between Saturday and Sunday nights. The dead include 72 residents of Shejaiya, one of Gaza’s poorest and most densely populated neighborhoods, where Israeli forces carried out their single worst attack so far. Survivors called the carnage a “massacre,” and U.N. Secretary-General Ban Ki-moon called it an “atrocious action.” Eighteen Israeli soldiers have died in Gaza since Thursday, when Israel launched a ground invasion it said was aimed at cutting off tunnels used by Hamas. Thirteen of the soldiers died fighting militants in Shejaiya.