The brother of al-Qaida leader Ayman al-Zawahiri has been arrested in a city across the Nile from Cairo, according to Egyptian security forces.
Mohammed al-Zawahri is the leader of the ultraconservative Jihadi Salafist group and is an ally of ousted Egyptian president Mohamed Mursi.
His arrest is not said to be related to terrorism.
Ayman al-Zawahiri has accused the US of overthrowing Mursi, but said the ousted president had brought it upon himself by trying to appease Washington.
Mohammed al-Zawahri, who is said to have commanded insurgents in the Sinai peninsula, was detained at a checkpoint in Giza.