Hundreds of members and supporters of the April 6 Youth Movement attended a press conference on Sunday to mark the campaign's six-year anniversary.
The conference, held at the Lawyer's Syndicate in downtown Cairo, focused on the movement's criticism of Egypt's interim authorities, including its recent crackdown on activists from the 25 January revolution and a protest law issued in November banning demonstrations not pre-approved by authorities.
They also demanded the release of political detainees.
"I am a lawyer and I'm proud of the [April 6] movement's presence in the syndicate [today]," human rights lawyer Gamal Eid said during the press conference.
Eid went on to denounce a defamation campaign targeting the youth movement, adding that "when those [responsible] were in their homes, April 6 [members] along with workers were taking down the photos of Hosni Mubarak."
The April 6 movement was established in 2008, when it called for a national strike in solidarity with a labour strike in the Nile Delta city of Mahalla and also against then-president Hosni Mubarak.
Members of April 6, along with other icons from the 2011 uprising that toppled Mubarak, have been targets of a recent smear campaign.
The latest wave of defamation came from TV anchor Abdel-Rehim Ali, host of a programme called "The Black Box" on private TV channel Al-Qahera Wal Nas. Over several episodes, Ali – who claims he possesses over 5,000 recordings – aired the private phone calls of several prominent activists that he claimed proved they had "conspired against state institutions."
Sunday's press conference was followed by a protest at the stairs of the nearby Journalist's Syndicate amid an absence of security personnel.
Hundreds held posters of detained activists and bars to symbolise prison cages.
Two of the movement's founders and current members, Ahmed Maher and Mohamed Adel, are currently appealing two-year sentences on charges of violating the protest law.
They have been in detention since last November.
In March, the April 6 Youth Movement launched a petition calling for the cancellation of the controversial protest law.
A march around downtown had also been planned for Sunday, but it was cancelled by organisers.
Hours before the press conference, military police closed all entrances to Tahrir Square, located around 1 km away from the lawyers and journalists' syndicates.