Alaa Abdel-Fattah was detained while on day release, having served five years in jail for staging an illegal protest in 2013. Fresh anti-government protests earlier this month prompted a harsh response from authorities.
Egyptian authorities on Sunday detained prominent dissident Alaa Abdel-Fattah beyond the terms of his probation, his family and a judicial official said.
The 37-year-old is subject to a day-release order that requires him to report to a Cairo police station every evening and remain in a cell overnight.
In March, Abdel-Fattah completed a 5-year jail sentence for staging an illegal demonstration in 2013 in the wake of the country's Arab Spring protests that led to the downfall of longtime leader Hosni Mubarak. His probation also lasts for five years.
His sister Mona Seif, also a well-known activist, said on Twitter: "We don't know where Alaa is ... The police station says he's most probably at state security prosecution ... we seriously don't have any information about him."
Abdel-Fattah told the Agence France-Presse news agency in June that he had twice been ordered to stop talking about his probation publicly or face being sent back to jail indefinitely.
His re-arrest comes after the detention of some 2,000 anti-government activists over the past week.
The arrests followed scattered protests on September 20 after an Egyptian businessman living in self-imposed exile leveled corruption allegations against the president and the military. The allegations were dismissed by President Abdel-Fattah el-Sissi as "sheer lies."
A security official told The Associated Press that Alaa Abdel-Fattah was taken to prosecutors for an investigation into claims that he had called for protests.
The official spoke on condition of anonymity because they were not authorized to brief media.
mm/jlw (AFP, AP)