Egyptian authorities have detained prominent opposition leader Hazim Abdelazim, three security sources told Reuters on Sunday.
Mr Abdelazim was arrested at his home in Cairo late on Saturday night on suspicion of publishing false news and inciting against the state, one source said.
Once a deputy telecoms minister under former president Hosni Mubarak, Mr Abdelazim was later heavily involved with Abdel Fattah El Sisi's successful 2014 election campaign where he chaired the youth committee.
The interior ministry could not be reached for comment.
Last week, Egyptian authorities arrested blogger and journalist Wael Abbas, accusing him of involvement with an illegal organisation and publishing false news.
Mr Sisi won a second term in office in a March election that featured only one other candidate - himself an ardent Sisi supporter - after all serious opposition contenders halted their campaigns citing intimidation and several arrests.
Former military commander Mr El Sisi was elected in 2014, a year after leading the army to the ousting of Islamist President Mohamed Mursi.