Family members of Egyptians detained for planning a demonstration last month say 21 of them have started a hunger strike, protesting what they call an "unfair trial".

Heba Mohamed, the wife of Egyptian detainee Nagi Kamel, told The Associated Press on Sunday that 10 of the 152 convicted started the hunger strike last week, with another 11 detainees joining them Saturday. She says a new group of detainees will be joining the strike every few days.

Egyptian courts convicted 152 protesters in a single day for breaking a law that bans demonstrations, sentencing them to up to five years in prison. The 152 were convicted for demonstrations planned on April 25 to protest the government's surrender to Saudi Arabia of two Red Sea islands.