Dozens of protesters gathered in Cairo's Tahrir Square on Friday afternoon to take part in a planned anti-Morsi rally in solidarity with the recently-launched 'Rebel' campaign. Three scheduled marches from Mostafa Mahmoud Square in the district of Mohandeseen, Dawaran Shubra Square in Shubra, and central Cairo's Sayyeda Zeinab Mosque have also started heading to Tahrir Square. Demonstrators in the marches numbered in the hundreds. 'Rebel' is a grassroots movement aimed at registering opposition to President Mohamed Morsi and forcing him to call early presidential elections by collecting as many as 15 million signatures by 30 June. Campaigners for the 'Rebel' signature drive said they aim to intensify their presence in the square to collect the maximum number of signatures, Egyptian state news agency MENA reported. Protesters have put up a platform in the centre of the square, and pictures of slain protesters can be seen in the square's central garden. Security has been tightened around the usual protest hotspots, including the interior ministry, the Cabinet headquarters, the Shura Council, the presidential palace and the Brotherhood headquarters. In Alexandria, hundreds of protesters have started heading to Qaid Ibrahim Square in support of the petition against President Morsi, condeming the "Brotherhoodisation of the state," Al-Ahram's Arabic-language news website reported. A number of political parties are participating in Friday's planned million man march, including the Constitution Party, the Free Egyptians Party, the Socialist Popular Alliance, the Karama Party, the Free Front for Peaceful Change, the Popular Current and the Kefaya movement. Major demands of the anti-government demonstration include snap presidential elections, the release of detained political activists, and a new constitution. Officially launched on 1 May, the 'Rebel' group said it has collected more than two million signatures in the first 10 days. Egypt's opposition has grown increasingly discontent with President Mohamed Morsi's Islamist-led regime's perceived attempts to monopolise state institutions and smother dissent. Opposition figures also criticsed Egypt's new constitution, which was drafted by an Islamist-dominated assembly and passed by popular referendum last year. Several political activists as well as media figures and journalists have been recently arrested or questioned over a range of charges, including inciting violence as well as insulting and defaming the president.