Ammar, 20-year-old son of Mohamed El-Beltagy, the former MP and senior leader of Egypt's Muslim Brotherhood, was arrested on Sunday as part of a large-scale crackdown on the Islamist movement.

Along with three other sons of Brotherhood leaders, Ammar El-Beltagy was rounded up in Beni Suef Governorate, south of Cairo, security sources said. His father, who was issued an arrest warrant on allegations including terrorising people, torture and murder, is still in hiding, as is leading Brotherhood member Essam El-Erian.

Mohamed El-Beltagy's 17-year-old daughter Asmaa was killed in a bloody police raid on the pro-Morsi protest camp in east Cairo on 14 August, which left dozens dead and sparked days of deadly clashes pitting Islamists and security forces.

The 85-year-old Muslim Brotherhood, which had operated in the shadows until the deposition of autocrat Hosni Mubarak in 2011 allowed it to officially emerge on the political scene, has been reeling from a broad clampdown on its upper echelon and supporters following the ouster of Brotherhood-affiliated president Mohamed Morsi last month.

Mohamed Badie, the group's top authority and spiritual leader, was arrested last week, making it the first time in three decades that the group's supreme guide is arrested.

Badie, along with his two deputies Khairat El-Shater and Rashad Bayoumi, are due to stand trial on 29 October after the first hearing was adjourned on Sunday because the defendants could not attend for security reasons.