Iran's paramilitary Revolutionary Guard threatened Sunday to launch its "most-intense offensive operation" ever after the killing of Supreme Leader Ayatollah Ali Khamenei. "The most-intense offensive operation in the history of the armed forces of the Islamic Republic of Iran will begin in moments, targeting (Israel) and American terrorist bases," it said. Mourners raised a black flag over the Imam Reza shrine in Mashhad, Iran's second-largest city and a major pilgrimage site for Shiite Muslims.