Newsweek. 15th October 2016.Exclusive: Private ISIS Letter Outlines Group's Merciless Tactics Ahead Of Mosul Battle The Islamic State militant group (ISIS) is as brutal in its private orders to its top commanders as it is in its public propaganda, according to a letter obtained by Newsweek, sent when the group was threatened in the northern Syrian city of Manbij in August. As ISIS fighters struggled to keep control of Manbij against encroaching U.S.-backed Kurdish and Arab forces, an unnamed emir of the group’s War Committee in Raqqa, its de facto capital, dispatched a three-page, handwritten communique to the top ISIS commander in the city, Abu Yahya al-Shami. The letter ordered al-Shami to execute defecting fighters, quash dissent in its ranks and imprison “bewitched” militants—a message analysts say the ISIS leadership will communicate to its commanders in Mosul in the face of a U.S.-Iraqi offensive that began on Monday. Read more.