Prosecutors have renewed the detention of leading activist Alaa Abdel-Fattah for a further 15 days, a judicial source told Ahram Online on Sunday.
He is accused of inciting demonstrations in breach of a new protest law.
Abdel-Fattah, a symbol of the 2011 uprising against president Hosni Mubarak, was arrested at his home on Thursday.
Authorities ordered his detention for four days on Friday.
April 6 Youth Movement founder Ahmed Maher, who was arrested on Saturday, was released earlier today.
Details of both decisions have yet to be released.
Abdel-Fattah and Maher were arrested for allegedly instigating protests on Tuesday in violation of a new protest law that proscribes demonstrations without prior police approval. They have also been charged with thuggery and incitement of violence.