Cairo: Egypt’s Muslim Brotherhood said on Saturday that a son of its spiritual leader was killed during fierce clashes in downtown Cairo, as hundreds of Islamists supporters of the country’s ousted president remained barricaded inside a mosque.

The group’s political arm, the Freedom and Justice party, said on its official website that Mohammad Badie’s son Ammar was killed on Friday. That’s when the Muslim Brotherhood took to the streets in a ‘Day of Rage’ — ignited by anger at security forces over clearing two sit-in camps protesting the ouster of President Mohammad Mursi, leaving hundreds dead.

The Muslim Brotherhood-led anti-military coalition has called for a week of protests, further escalating unrest in the country. The coalition says that they won’t back down until it topples the government installed by the military — which overthrow Mursi on July 3.

Meanwhile, an Egyptian security official says the brother of Al Qaida chief Ayman Al Zawahri has been arrested in Egypt.

The official said on Saturday that Mohammad Al Zawahri, leader of the ultraconservative Jihadi Salafist group, was detained at a checkpoint in Giza, the city across the Nile from Cairo.

The official declined to give further details. He spoke anonymously as he was not authorised to speak to the press.

Mohammad Al Zawahri’s group espouses a hardline ideology but was not clandestine prior to Egypt’s July 3 coup. He was allied with Mursi.

Authorities said earlier that Al Zawahri had commanded insurgents in Sinai Peninsula.