GAZA/JERUSALEM—Israel said it killed 16 members of the Hamas military wing in an airstrike on Gaza on Wednesday and Palestinian militants rained rockets into Israel as global concern mounted over their most intense hostilities in years. At least 53 people have been killed in Gaza since violence escalated on Monday, according to the Palestinian territory’s health ministry. Six people have been killed in Israel, medical officials said. Israel’s Shin Bet security service said the brigade commander for Gaza City was among senior members of the Islamist militant group Hamas who had been killed. “This is just the beginning. We’ll hit them like they’ve never dreamed possible,” Prime Minister Benjamin Netanyahu said in a statement. Soon after the announcement, a new rocket barrage was fired at the Israeli city of Ashdod and Israeli media said the military was preparing for new salvoes on the Tel Aviv area. Hamas confirmed the commander’s …