Egyptian authorities on Tuesday arrested Mohammed Badie, supreme guide of the Muslim Brotherhood, who had been in hiding since the Brotherhood's Mohammed Morsi was ousted as president in early July.
An Interior Ministry official told dpa that Badie was arrested in an apartment in Rabaa al-Adawiya, the Cairo district where a sit-in by Morsi supporters was broken up by police on Wednesday leaving hundreds dead.
Pro-government OnTV broadcast what it said were live pictures of Badie in custody, while state television's website showed photographs of the Islamist leader in a police truck.
Badie's son Ammar was killed on Friday when a pro-Morsi protest degenerated into violent clashes between police and demonstrators on a day that saw 173 die, according to official figures.
The leader of the conservative Islamist group, founded in 1929, did not attend the funeral.
Egyptian prosecutors reportedly issued an arrest warrant for Badie on July 4 on charges of inciting the killing of demonstrators.
Despite reports of his arrest, Badie two days later gave a fiery speech to tens of thousands of Morsi supporters at Rabaa al-Adawiya.
"The millions supporting Morsi will stay in the squares until the president of Egypt is reinstated," Badie told cheering crowds. He had not been seen since.
Badie was one of the few senior Muslim Brotherhood officials not yet in custody as prosecutors have issued a string of arrest warrants for the movement's leaders.
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