A security official said that Mohammed al-Zawahri, leader of the ultraconservative Jihadi Salafist group, was detained at a checkpoint in Giza, the city across the Nile from Cairo.

Ayman al-Zawahri is credited by many as having been the ‘operational brains’ behind the 9/11 suicide attacks on the U.S. and to have approved the co-ordinated bombings on London’s transport system in in 2005 that left 52 innocent people dead.

Mohammed Al-Zawahri’s group espouses a hard-line ideology but was not clandestine prior to Egypt’s July 3 coup.

He was allied with ousted President Mohammed Morsi, an Islamist, whose supporters are now taking to the streets to protest the killings of its supporters in a security crackdown last week.