A son of Muslim Brotherhood leader Mohammed Badie was killed in Cairo during Friday's "Day of Rage" protests against the army-backed Egyptian government, the Brotherhood's Freedom and Justice Party said.
Ammar Badie, 38, died of a bullet wound sustained while taking part in protests in Ramses Square, it said on its Facebook page.
The whereabouts of Mohamed Badie, who is the Islamist movement's General Guide, are unknown. He has been charged with inciting violence and faces a trial that starts on Aug. 25. His son's death follows the killing of the daughter of Mohamed El-Beltagi, a senior Brotherhood politician, in protests this week.
Egyptian state TV also reported on Saturday that the son of Hassan Malek, another Brotherhood leader, had been arrested.
Police also detained Brotherhood politician Gamal Heshmat, according to a statement from the Anti Coup Alliance. Heshmat is a leading member of the Freedom and Justice Party.
The fiercest street clashes Cairo has seen in more than two years of turmoil left at least 82 people dead, including 10 policemen.
Egyptian authorities said they arrested 1,004 "elements" of the Muslim Brotherhood during nationwide protests on Friday.
Want to enjoy 'Zen' reading - with no ads and just the article? Subscribe todaySubscribe now