CAIRO (AP) — The lawyer for a former diplomat who called for a referendum on Egyptian President Abdel-Fattah el-Sissi's government has been arrested.

Khaled Ali says he was told by Masoum Marzouk's family that he was taken from his home on Thursday and that his whereabouts are unknown.

Marzouk called for the referendum earlier this month and proposed a roadmap for a political transition if Egyptians voted against the government. He said if the government did not respond positively to the initiative he would hold a "popular conference" in Cairo's Tahrir Square — epicenter of the 2011 uprising — on Aug. 31.

El-Sissi was re-elected in March after all serious challengers were either arrested or pressured into leaving the race. His government has waged a sweeping crackdown on dissent in recent years.