The burgeoning list of appalling acts by ISIS has grown even longer: The Islamic extremist group has blown up a nearly 2,000-year-old temple in the historic ruins of Palmyra, Syria.

UNESCO, the United Nations cultural organization, called the destruction of the Temple of Baalshamin a "war crime."

Maamoun Abdulkarim, Syria's director-general of antiquities and museums, said Sunday that sources in Palmyra informed him that ISIS members rigged the temple with large quantities of explosives and detonated them.