Leading Muslim Brotherhood figure Mohammed al-Beltagi has been arrested, according to Egyptian officials.
Mr Beltagi, secretary-general of the Brotherhood's Freedom and Justice Party (FJP), is accused of inciting violence, state media said.
Former labour minister Khaled al-Azhari was also held.
It comes as Egypt's military moves against Brotherhood leaders following the ousting of former President Mohammed Morsi.
Prosecutors had ordered the arrest of Mr Beltagi on 10 July.