CAIRO — A former Egyptian diplomat who called for a referendum on President Abdel-Fattah el-Sissi's government and threatened to organize a gathering in Cairo's Tahrir Square was arrested on Thursday.

Security forces searched Masoum Marzouk's home before taking him away, his daughter, Maisara, said. An Egyptian security official said he faces charges of belonging to an outlawed group that aims to overthrow the government and disrupt the constitution. The official spoke on condition of anonymity because he was not authorized to brief the media.

Marzouk, who served in the Egyptian army's special forces, is a veteran of the 1973 war against Israel. He later held several diplomatic posts throughout his career, including as ambassador to Finland, Estonia and Uganda, and assistant to the foreign minister for African affairs.

Earlier this month, Marzouk had called for a referendum and proposed a political roadmap if Egyptians voted against the government. The transition would have included the suspension of the constitution, the termination of the current presidential term and the dissolution of parliament, which is packed with el-Sissi supporters. Marzouk said if the government rejected his proposal he would hold a "popular conference" in Tahrir Square — epicenter of the 2011 uprising — on Aug. 31.

El-Sissi was re-elected for a second four-year term in March after all serious challengers were either arrested or pressured into leaving the race. He led the 2013 military ouster of Islamist President Mohammed Morsi following mass protests against his divisive yearlong rule.

Authorities have waged a sweeping crackdown on dissent in recent years, jailing thousands of dissidents and rolling back freedoms won in the 2011 uprising. The government has banned unauthorized protests, heavily restricted civil society groups and blocked hundreds of websites.

Khaled Ali, a prominent human rights lawyer who is representing Marzouk, said other critics of the government were also arrested Thursday, including Yehia al-Qazzaz, a geology professor, and Raied Salama, an economist. Ali had planned to run against el-Sissi in this year's election but withdrew, saying the climate was not conducive to campaigning.

Austerity measures aimed at rebuilding the economy after years of unrest have meanwhile taken a heavy toll on poor and middle-class Egyptians. With virtually all other avenues of dissent shut down, Egyptians have taken to social media to vent their criticism of the government, with a popular hashtag calling on el-Sissi to resign.

El-Sissi recently said he was "upset" over the online calls for him to step down.