Maasoum Marzouk also proposed release of all political prisoners and protests at Tahrir Square if demands weren’t met.

Egyptian authorities arrested a former diplomat and two others in Cairo in the face of planned protests in Tahrir Square calling for a referendum on President Abdel Fattah el-Sisi’s rule.

The arrest of Maasoum Marzouk on Thursday came after he also proposed the release of all political prisoners, the formation of a transitional government council, and a 10-year ban on political candidacy for anyone who served in government or parliament over the past 10 years.

Marzouk declared in an August 5 statement that if his initiative was not accepted, he would hold a “popular conference” in Tahrir Square on August 31 to “discuss next steps”. Tahrir was the epicentre of the 2011 mass uprising that led to the downfall of former President Hosni Mubarak.

Marzouk, who served in the Egyptian army’s special forces, is a veteran of the 1973 war against Israel. He is also a former Egyptian ambassador to Uganda, Finland and Estonia, and was assistant minister of foreign affairs under Mubarak.

He recently helped found The People’s Democratic Party and served as an adviser and spokesman for the presidential campaign of Hamdeen Sabbahi, a leftist candidate who ran against Sisi in the 2014 elections.

Following his statement, a complaint was filed against Marzouk with charges including “insulting the state” and “promoting chaos”.

Khaled Ali, Marzouk’s lawyer, said police officers besieged his Cairo home and took him to an unknown location.

He also confirmed the arrest of economist Raed Salama and geology professor Yahia Kazzaz on Thursday. The charges against them remain unclear.

Sisi won a second four-year term in April after securing 97 percent of the vote in the presidential election.

The election was criticised as a one-man show with no credible opposition. At least six other candidates were either jailed, prosecuted, or pulled out of the race.