April 6 Youth Movement has demanded the release of its members who were arrested on Monday while attempting to commemorate the first anniversary of their colleague's killing.
Police said they arrested the activists because they were organising an illegal demonstration.
The youth group said it was planning a memorial for Ahmed El-Masry at his family's residence in Giza's Boulaq El-Dakrour district when police "ambushed" them and arrested around 13 people and transferred them to a Central Security Forces' camp.
El-Masry was shot dead one year ago while covering the police's dispersal of the Muslim Brotherhood's Nahda Square protest camp in Giza's Mohandiseen.
The group’s statement said it had not violated the law, adding that it held the interior ministry responsible for any harm to those currently being detained.
Two members of the group's political bureau, Mohamed Kamal and Khaled Ismail, were among those arrested.
Other leading members of the movement, Ahmed Maher and Mohamed Adel, are currently serving three-year prison sentences on charges of holding an unauthorised protest.
A protest law, passed in November 2013, mandates that protests must receive prior approval from the interior ministry. Violators face hefty fines and prison sentences.
Opposition political groups and parties have called for the law to be changed.
Hundreds of supporters of ousted president Mohamed Morsi have been arrested for breaking the protest law. Several leftist activists are also facing harsh prison sentences under the new law, including Alaa Abdel-Fattah, Mahinour El-Masry and Popular Current member Ahmed Douma.
Several imprisoned activists have started a hunger strike to protest their detention.