Prosecutors have ordered the detention of 24 activists for four days after they were arrested at unauthorised demonstrations on Tuesday, judicial sources have told Ahram Online.
The interior ministry initially said police had arrested 52 people during a protest against military trials of civilians and the new assembly law. They later said the number was 28.
Twenty-six arrested women were released on a desert road later on Tuesday, activists said via Twitter.
A number of journalists were also released.
Teargas and water cannon were used to disperse hundreds of protesters at the Shura Council, and at a separate protest outside the press syndicate to commemorate the earlier killing of a protester by police.
The protests were held in defiance of a new law requiring police approval for protests.
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 sought prior permission.
A number of prominent activists – including lawyer Zyad El-Elaimy – turned themselves in to police shortly after the demonstration, in solidarity with the protest organisers.
El-Elaimy said they were questioned by prosecutors late on Tuesday.
Among those arrested were Mona Seif, founder of a campaign against military trials of civilians, and Ahmad Harara, an activist who lost his eyes to birdshot during protests against former president Hosni Mubarak in 2011 and the military junta that took power after Mubarak's fall.
A number of groups have said they will hold further demonstrations on Wednesday against the protest law and police abuses.
The police measures sparked condemnation from many observers.
Thirteen members of the panel drafting Egypt's new constitution have suspended their work in protest at the detentions, Al-Ahram Arabic news website reported.
Dozens of lawyers have begun an open-ended strike at the lawyers' syndicate in protest at the arrests, according to Al-Ahram.
The United States, which has partially suspended aid to Egypt, on Monday voiced alarm at the protest law, saying it does not meet international standards and hampers the country's progress towards democracy. The UN has slammed it as "seriously flawed" and urged the interim authorities to amend it.
The interim government has said it is not against peaceful protests but seeks to restore order in a country rocked by political tumult since the ouster of Islamist president Mohamed Morsi in July.