Egyptian prosecutors ordered the detention of 24 protesters arrested on Tuesday for 15 further days, judicial sources told Ahram Online.
The protesters are charged with breaking a new law that regulates protests and demonstrations.
On Tuesday, security forces used teargas and water cannon to disperse hundreds of protesters at two demonstrations in downtown Cairo.
The protests were held in defiance of a new law requiring police notification in advance for any demonstrations.
Under the legislation, the interior ministry can ban gatherings of more than ten people, and breaking the law can result in jail sentences and hefty fines.
Security officials said Tuesday's rallies were broken up because protest organisers had not made notifications.
Prominent activists Alaa Abdel-Fattah and 6 April Youth Movement leader Ahmed Maher have said they will hand themselves in to the prosecutor-general on Saturday to answer to accusations of inciting Tuesday's protests.
The prosecution refused to charge other activists who told prosecutors that they had called for the protest without requesting the police's authorisation, in a move to challenge the law.