Malek Adly's detention came amid a wave of arrests in Egypt as security forces put down protests against President Abdel-Fattah el-Sissi decision on the islands.
Adly, a member of the April 6 youth movement that was part of the uprising that toppled longtime autocrat Hosni Mubarak in 2011, has appeared on TV talk shows, speaking out against the islands' handover. He was also among a group of lawyers who filed a lawsuit over the case of the islands.
Both el-Sissi and Abdel-Ghaffar have ignored the demands. The interior minister on Thursday attended the inauguration of a mega project for land reclamation hailed by el-Sissi as one of his "unprecedented" achievements. In his half-an-hour speech at the event, el-Sissi repeated several times, "I am not afraid" a statement observers believe was meant for his critics.
Later yesterday, another well-known Egyptian rights advocate and lawyer, Ragia Omran, was detained at the Cairo International Airport upon her arrival from Jordan, where she attended a UN conference.
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Omran is a member of the National Council for Human Rights, and has been one of the main defenders of imprisoned political activists.
The Interior Ministry spokesman did not answer phone calls seeking comment. Airport security officials said that Omran was stopped at the airport over allegations linking her to "incitement" against the state, undermining state security and safety and that she is currently being interrogated. The officials, speaking on condition of anonymity under regulations, added that her name has been on an airport stop-list.
A draconian anti-protest law issued months later led to mass arrests of thousands of protesters, mostly Morsi's supporters or pro-democracy advocates. The law and heavy-handed security measures have stifled street demonstrations.