Opposition activists are claiming more than 300 people were killed in Syria’s violence on Wednesday, the highest single-day toll of the 18-month-old conflict to date. The killings include an alleged massacre in the town of Dhiyabia, where some 40 people were reportedly slain. Video released by opposition activists shows rows of bloodied corpses covered in blankets. The United Nations’ refugee agency meanwhile is warning up to 700,000 people may wind up fleeing Syria by the end of the year, far greater than the previous estimate. Some 294,000 refugees have already left Syria this year.