Islamic State militants in Syria committed an “intolerable crime against civilization” by destroying the Temple of Bel, one of the ancient world’s most iconic monuments, the head of the U.N. cultural agency said Tuesday. The militants used explosives to destroy the two-millennia-old temple in the ancient city of Palmyra on Sunday. Witnesses described a huge blast and the destruction was later confirmed by U.N. satellite images. Over the past year, IS has seized one-third of Iraq and Syria and imposed a violent interpretation of Islamic law in a self-declared “caliphate” straddling the two countries. The group captured the ruins of Palmyra and an adjacent modern town of the same name in May.