The U.S. military said Wednesday it has started transferring detainees from the Islamic State group being held in northeastern Syria to secure facilities in Iraq.

The move came after Syrian government forces took control of a sprawling camp, housing thousands of mostly women and children, from the U.S.-backed Syrian Democratic Forces, or SDF, which withdrew as part of a ceasefire. Troops on Monday seized a prison in the northeastern town of Shaddadeh, where some IS detainees escaped and many were recaptured, state media reported.