Egyptian authorities have arrested the brother of al-Qaeda chief Ayman al-Zawahri, security officials said.

Mohammed al-Zawahri, leader of a Salafist group, was detained at a checkpoint in Giza, the city across the Nile from Cairo.

Mohammed al-Zawahri's group espouses a hardline ideology but was not clandestine prior to the military takeover on July 3.

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

The official news agency, MENA, confirmed the arrest.

Authorities said earlier that Mohammed al-Zawahri had commanded fighters in Sinai Peninsula.

He was detained as part of a round up of more than than 1,000 Islamists in the country. The round up, announced by the authorities, was conducted after Friday's protests.

Mohammed al-Zawahiri had been seen in Cairo in January at protests outside the French Embassy by hundreds of Salafists against the French military campaign in Mali.