Siddig told "Bidoun" magazine that there was an increased demand for Islamic and Arabic character roles in both film and television after the September 11 attacks and that people began to approach him with projects within six months of the event. He played a mountain guide in the thriller film "Vertical Limit" (2000), starring Chris O'Donnell, and Ajay in the post-apocalyptic science fantasy film "Reign of Fire" (2002) starring Christian Bale. In 2003 Siddig played the role of an Algerian secret agent on the trail of Islamists in the controversial episode "Nest of Angels" of the British television show "Spooks" (known as "MI-5" in the US.) Siddig appeared in a cameo role as Khalid Sheikh Mohammed the film "The Hamburg Cell" that premiered the following year.