Syria rebels 'seize' ISIS headquarters in Aleppo 8 January 2014 Last updated at 11:13 Islamist rebel brigades are reported to have seized the headquarters of Islamic State in Iraq and the Levant (ISIS) in the northern Syrian city of Aleppo. The Syrian Observatory for Human Rights said it was not clear what had happened to the jihadists who had been at the former hospital in the Qadi Askar area. A video posted online showed rivals proclaiming their victory there. Recent days have seen fierce fighting in several Syrian towns between the al-Qaeda affiliate and other rebel groups. On Tuesday evening, an ISIS spokesman vowed that it would "crush" its rivals and "kill the conspiracy in its cradle." Abu Mohammed al-Adnani also said it considered members of the opposition alliance, the National Coalition, and the Supreme Military Council of the Western-backed Free Syrian Army as "legitimate targets."