Egypt's April 6 youth movement said Tuesday it will appeal a court ban of the movement, which spearheaded the 2011 uprising against Hosni Mubarak, accusing authorities of silencing dissent.
And it said it would continue its activities despite the ban.
The Monday court ruling was based on a complaint accusing the group of defaming the country and colluding with foreign parties.
April 6 also opposed Islamist president Mohamed Morsi, who was toppled by the army in July, but turned on the military-installed regime when the authorities cracked down on dissidents.
"The current regime wants to monopolise power and silence any voice of real opposition" Mohamed Kamal, a member of the movement's political office, told a press conference.
He said the group will appeal what he called "a politicised ruling" and continue operating.
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Mohamed Fuad, a spokesman of "April 6-Democratic Front," an offshoot of the April 6 movement, said authorities, not the youth group, were defaming the country.
He cited the adoption of a law banning all but police-sanctioned protests and the hundreds of death sentences handed Monday to Morsi's supporters after a rushed mass trial in the southern province of Minya.
Secular-leaning groups such as April 6 have increasingly protested against the government, accusing it of restricting freedom while giving police a free hand to crush dissent.
In December, April 6 leader Ahmed Maher was jailed for three years in for violating the law that bans all but police-sanctioned protests.
Since the army ousted Morsi amid a wave of protests, a crackdown targeting his supporters has left more than 1,400 dead and 15,000 in jail.
Hundreds of Morsi's supporters have been sentenced to death or life imprisonment.