Philip Rizk, 26, a graduate student at the American University in Cairo, was detained by police Friday night while returning to Cairo from Qalyoubia, north of Cairo, his sister Jeanette told Reuters.
Rizk and a group of activists had been holding a march in the rural areas north of Cairo in solidarity with Palestinians and to raise awareness about the effects of Israeli occupation of Palestinian territories, according to Salma Said, an activist who was with Rizk when he was detained.
A spokesman for the Ministry of Interior said he had received no word of the detention.
Said said police had detained their vehicle for several hours and then said they wanted to talk with Rizk. They put him in a vehicle with no licence plates and sped off. Other policemen then blocked the activists' vehicle to prevent them from following.
"We don't know where he is, and there is no formal charge," Rizk's sister said. She added that the German embassy had been notified and were attempting to locate him.
Rizk, who blogs at Tabula Gaza (http://tabulagaza.blogspot.com) is "passionate" about Gaza and had recently completed most of the work on a short documentary about non-violent resistance to Israeli occupation, according to his sister.
She said that Rizk, who lived in Gaza for two years, had been helping get medicine into the coastal enclave that was recently the target of a 22-day Israeli offensive that left more than 1,300 Palestinians dead.